Let's start running the tests under `engine/` using the CanvasKit renderer instead of HTML.

This PR also:
- Moves several tests from `engine/` to `html/` since they were testing html-specific stuff.
- Deletes `test/canvaskit/semantics_test.dart` since it's just an "alias" for `test/engine/semantics/semantics_test.dart`.

#57153)

Migrates Layers and LayerTree and parts of the `flow/` utility classes to use DlGeometry (Impeller) classes.

Use FlMockBinaryMessenger instead of mocking the whole engine.

Use FlMockBinaryMessenger instead of mocking the whole engine.

…... (#57163)

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Add missing tests for this function.

Note this makes FlKeyboardManager a bit more complex, but this is
planned to be simplified in a future refactor.

…57105)

We can use a macro to distinguish between all of the blend modes. We don't need to distinguish between porter duff/ advanced /pipeline as the pipeline is already labeled with the shader used.

For all snapshots the additional label on the texture isn't useful since we can just look at the command.

fixes flutter/flutter#160180

I'm unable to reproduce the problem locally but this is the most likely cause.

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There are only 3 or 4 sampler's active at any given time in a flutter app. rather than store them in a hashmap, just use a vector.

test exempt: should have no functional change

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…recursively (#57168)

The original workaround ([PR](#56804)) works for the official web view plugin, but it doesn't work for a third party plugin `flutter_inappwebview` ([issue](https://github.com/pichillilorenzo/flutter_inappwebview)). Upon discussion with the author of that plugin, it turns out that their platform view is not a WKWebView, but rather a wrapper of WKWebView. 

This PR performs a DFS search of the view hierarchy, and enable the workaround as long as there's a WKWebView inside. 

TODO: pending sample project:
I am quite positive that it should work, but **I haven't tried it since I don't have a sample project yet**. I have requested a sample project with them so I can verify the solution. 

*List which issues are fixed by this PR. You must list at least one issue.*

 pichillilorenzo/flutter_inappwebview#2415

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A flaw in #57153 - SkRRect would normalize the rect (make it right-side up), a feature that Flutter code takes advantage of. We need to do that manually when we ingest a round rect from Flutter.