…multi-view rendering (flutter/flutter#125003)

…multi-view rendering (flutter/flutter#125003)

…multi-view rendering (flutter/flutter#125003)

…multi-view rendering (flutter/flutter#125003)

…multi-view rendering (flutter/flutter#125003)

…multi-view rendering (flutter/flutter#125003)

…multi-view rendering (flutter/flutter#125003)

As of flutter/flutter#125003 the current method
these tests use to get the screen width throws an exception, since it
assumes that the first widget in the tree has certain properties. To
make the test more robust, this get the width of the outmost Column,
which is part of the test setup, rather than whatever the first widget
is.

Unblocks the flutter->packgaes roller.

As of flutter/flutter#125003 the current method these tests use to get the screen width throws an exception, since it assumes that the first widget in the tree has certain properties. To make the test more robust, this get the width of the outmost Column, which is part of the test setup, rather than whatever the first widget is.

Unblocks the flutter->packgaes roller.

…multi-view rendering (flutter/flutter#125003)

Manual roll requested by [email protected]

flutter/flutter@f842ed9...6f09064

2023-07-17 [email protected] Stand-alone widget tree with multiple render trees to enable multi-view rendering (flutter/flutter#125003)
2023-07-17 [email protected] Update to valid build tools variant and update lockfiles (flutter/flutter#125825)
2023-07-17 [email protected] Roll Packages from 369ee7e to 6889cca (5 revisions) (flutter/flutter#130721)
2023-07-17 [email protected] [Reland] - Update `DialogTheme` tests for M2/M3 (flutter/flutter#130711)
2023-07-17 [email protected] Roll Flutter Engine from 683087731feb to e4cae43c9c7a (9 revisions) (flutter/flutter#130716)
2023-07-17 [email protected] [flutter_tools] Support coverage collection for dependencies (flutter/flutter#129513)
2023-07-17 [email protected] Fix `DatePicker` uses incorrect overlay color from `DatePickerTheme` and add missing tests (flutter/flutter#130584)
2023-07-17 [email protected] Update `DropdownMenu`, `SnackBarTheme` and `Stepper` tests for M2/M3 (flutter/flutter#130464)
2023-07-17 [email protected] Clarify the whole "CustomPainters default to Size.zero" thing. (flutter/flutter#130624)
2023-07-16 [email protected] Update list of CoC contacts. (flutter/flutter#130630)
2023-07-15 [email protected] Manual roll Flutter Engine from 403866d16137 to 683087731feb (16 revisions) (flutter/flutter#130666)

If this roll has caused a breakage, revert this CL and stop the roller
using the controls here:
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…ew rendering (flutter#125003)

This change enables Flutter to generate multiple Scenes to be rendered into separate FlutterViews from a single widget tree. Each Scene is described by a separate render tree, which are all associated with the single widget tree.

This PR implements the framework-side mechanisms to describe the content to be rendered into multiple views. Separate engine-side changes are necessary to provide these views to the framework and to draw the framework-generated Scene into them.

## Summary of changes

The details of this change are described in [flutter.dev/go/multiple-views](https://flutter.dev/go/multiple-views). Below is a high-level summary organized by layers.

### Rendering layer changes

* The `RendererBinding` no longer owns a single `renderView`. In fact, it doesn't OWN any `RenderView`s at all anymore. Instead, it offers an API (`addRenderView`/`removeRenderView`) to add and remove `RenderView`s that then will be MANAGED by the binding. The `RenderView` itself is now owned by a higher-level abstraction (e.g. the `RawView` Element of the widgets layer, see below), who is also in charge of adding it to the binding. When added, the binding will interact with the `RenderView` to produce a frame (e.g. by calling `compositeFrame` on it) and to perform hit tests for incoming pointer events. Multiple `RenderView`s can be added to the binding (typically one per `FlutterView`) to produce multiple Scenes.
* Instead of owning a single `pipelineOwner`, the `RendererBinding` now owns the root of the `PipelineOwner` tree (exposed as `rootPipelineOwner` on the binding). Each `PipelineOwner` in that tree (except for the root) typically manages its own render tree typically rooted in one of the `RenderView`s mentioned in the previous bullet. During frame production, the binding will instruct each `PipelineOwner` of that tree to flush layout, paint, semantics etc. A higher-level abstraction (e.g. the widgets layer, see below) is in charge of adding `PipelineOwner`s to this tree.
* Backwards compatibility: The old `renderView` and `pipelineOwner` properties of the `RendererBinding` are retained, but marked as deprecated. Care has been taken to keep their original behavior for the deprecation period, i.e. if you just call `runApp`, the render tree bootstrapped by this call is rooted in the deprecated `RendererBinding.renderView` and managed by the deprecated `RendererBinding.pipelineOwner`.

### Widgets layer changes

* The `WidgetsBinding` no longer attaches the widget tree to an existing render tree. Instead, it bootstraps a stand-alone widget tree that is not backed by a render tree. For this, `RenderObjectToWidgetAdapter` has been replaced by `RootWidget`.
* Multiple render trees can be bootstrapped and attached to the widget tree with the help of the `View` widget, which internally is backed by a `RawView` widget. Configured with a `FlutterView` to render into, the `RawView` creates a new `PipelineOwner` and a new `RenderView` for the new render tree. It adds the new `RenderView` to the `RendererBinding` and its `PipelineOwner` to the pipeline owner tree.
* The `View` widget can only appear in certain well-defined locations in the widget tree since it bootstraps a new render tree and does not insert a `RenderObject` into an ancestor. However, almost all Elements expect that their children insert `RenderObject`s, otherwise they will not function properly. To produce a good error message when the `View` widget is used in an illegal location, the `debugMustInsertRenderObjectIntoSlot` method has been added to Element, where a child can ask whether a given slot must insert a RenderObject into its ancestor or not. In practice, the `View` widget can be used as a child of the `RootWidget`, inside the `view` slot of the `ViewAnchor` (see below) and inside a `ViewCollection` (see below). In those locations, the `View` widget may be wrapped in other non-RenderObjectWidgets (e.g. InheritedWidgets).
* The new `ViewAnchor` can be used to create a side-view inside a parent `View`. The `child` of the `ViewAnchor` widget renders into the parent `View` as usual, but the `view` slot can take on another `View` widget, which has access to all inherited widgets above the `ViewAnchor`. Metaphorically speaking, the view is anchored to the location of the `ViewAnchor` in the widget tree.
* The new `ViewCollection` widget allows for multiple sibling views as it takes a list of `View`s as children. It can be used in all the places that accept a `View` widget.

## Google3

As of July 5, 2023 this change passed a TAP global presubmit (TGP) in google3: tap/OCL:544707016:BASE:545809771:1688597935864:e43dd651

## Note to reviewers

This change is big (sorry). I suggest focusing the initial review on the changes inside of `packages/flutter` first. The majority of the changes describe above are implemented in (listed in suggested review order):

* `rendering/binding.dart`
* `widgets/binding.dart`
* `widgets/view.dart`
* `widgets/framework.dart`

All other changes included in the PR are basically the fallout of what's implemented in those files. Also note that a lot of the lines added in this PR are documentation and tests.

I am also very happy to walk reviewers through the code in person or via video call, if that is helpful.

I appreciate any feedback.

## Feedback to address before submitting ("TODO")

So, uhm, 2 years ago in #116429 we introduced this concept of a lookup boundary to hide certain InheritedWidgets in widget subtrees who belong to a different render tree than the InheritedWidget itself. This is for example needed for the Material widget: Buttons reach out to their Material ancestor to draw ink splashes on its associated render object. This only produces the desired effect if the button render object is a descendant of the Material render object (the two need to be in the same render tree). Overlay widgets have a similar problem. 

Lookup boundaries were specifically designed for multi view support, where a sub view would be powered by a separate and independent render tree. Ergo, widgets in the sub view shouldn't see these InheritedWidgets if they are part of the parent view. After all, it would be strange if clicking on a button in a subview draws the ink splash effect into the parent view. Unfortunately, we (and by that I really mean I) forgot to put a LayoutBoundary into the relevant multi view widgets when those were introduced in #125003. This PR addresses that by wrapping the `ViewAnchor.view` child in a LookupBoundary so that its subtree (which bootstraps a separate render tree) cannot see these InheritedWidgets in the parent view.

So, uhm, 2 years ago in flutter#116429 we introduced this concept of a lookup boundary to hide certain InheritedWidgets in widget subtrees who belong to a different render tree than the InheritedWidget itself. This is for example needed for the Material widget: Buttons reach out to their Material ancestor to draw ink splashes on its associated render object. This only produces the desired effect if the button render object is a descendant of the Material render object (the two need to be in the same render tree). Overlay widgets have a similar problem. 

Lookup boundaries were specifically designed for multi view support, where a sub view would be powered by a separate and independent render tree. Ergo, widgets in the sub view shouldn't see these InheritedWidgets if they are part of the parent view. After all, it would be strange if clicking on a button in a subview draws the ink splash effect into the parent view. Unfortunately, we (and by that I really mean I) forgot to put a LayoutBoundary into the relevant multi view widgets when those were introduced in flutter#125003. This PR addresses that by wrapping the `ViewAnchor.view` child in a LookupBoundary so that its subtree (which bootstraps a separate render tree) cannot see these InheritedWidgets in the parent view.