Do not send traversal child semantics nodes to engine when traversal parent is missing - #193372

…parent is missing (flutter#193372)

fix flutter#190357 
When an `OverlayPortal` (such as the one inside a Material `Slider`) is
inside a pushed route, the route's entrance transition (e.g.,
`FadeTransition`) starts at opacity `0.0` on the initial frame.

`RenderAnimatedOpacityMixin.visitChildrenForSemantics` skips visiting
the `OverlayPortal` anchor (`traversalParentIdentifier`), while
`_RenderTheater.visitChildrenForSemantics` still visits the
`OverlayPortal`'s `_RenderDeferredLayoutBox`
(`traversalChildIdentifier`) directly on the `OverlayEntry`.

Although the traversal child is excluded from its hit-test parent's
`childrenInTraversalOrder` and `childrenInHitTestOrder` when its
traversal parent is not in `_traversalParentNodes`,
`SemanticsOwner.sendSemanticsUpdate` still serialized the traversal
child via `_addToUpdate`. This sent an orphan `SemanticsNode` (not
referenced by any parent in the update) to the engine, causing issues.


This PR:
- Skips calling `_addToUpdate` in `SemanticsOwner.sendSemanticsUpdate`
for nodes in a traversal child subtree whose traversal parent is missing
(`_isSkippedInHitTestTree`).
- Marks affected traversal children, their unmerged descendants, and
their hit-test `parent`s dirty when a traversal parent is newly
registered, detaches, or changes its identifier so the nodes and
hit-test child lists are updated in sync when the traversal parent
enters or leaves the semantics tree.


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…279)

Material's Slider always wraps its value indicator in an OverlayPortal. In
a pushed route Flutter 3.47 then sends the engine a semantics node that no
parent lists as a child (flutter/flutter#190357). The macOS and Windows
accessibility bridges reject it, stay failed, and freeze their native tree
on stale nodes; a later pointer move can then read a freed node and crash
(flutter/flutter#193588). Part of #267.

NavisSlider wraps Slider in its own Overlay.wrap(alwaysSizeToContent,
Clip.none), which keeps the portal's semantics inside the slider. All 17
Slider sites use it and an architecture test forbids a bare Slider in lib.
The wrap goes away once a stable Flutter ships flutter/flutter#193372.

Co-authored-by: khalifa <[email protected]>
Co-authored-by: Claude Sonnet <[email protected]>