[WIP] Annotator tree (Step 1)

[dkwingsmt]

Description

An annotator tree is a tree built during painting, consisting of annotators, which can generate annotations when searched. This replaces the existing layer-based annotations.

For background, reasoning, and detailed design, see https://flutter.dev/go/annotator-tree.

As the first of the two steps of the annotator tree, this PR introduces the following changes:

• Adds the annotator API
  • Push an annotator during RenderObject.paint using PaintingContext.pushAnnotator()
  • Find an annotation between frames using RenderView.search() and RenderView.searchFirst()
• Deprecates legacy APIs
  • Layer.find
  • Layer.findAnnotations
  • Layer.findAll
  • Layer.findAllAnnotations
  • PlatformViewLayer.{constructor}.hoverAnnotation
  • PlatformViewLayer.hoverAnnotation
  • AnnotatedRegionLayer
• Introduces several APIs that are born deprecated

Most behaviors should be compatible, except for some trivial APIs. However, everything marked deprecated should be fixed soon as they will be removed in step 2.

#41194 is not solved for now due to compatibility, but will be solved in step 2.

Related Issues

• Step one of Move annotations to a separate tree #49568

Tests

I added the following tests:

• Tests

Checklist

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• I read the Contributor Guide and followed the process outlined there for submitting PRs.
• I signed the CLA.
• I read and followed the Flutter Style Guide, including Features we expect every widget to implement.
• I read the Tree Hygiene wiki page, which explains my responsibilities.
• I updated/added relevant documentation (doc comments with ///).
• All existing and new tests are passing.
• The analyzer (flutter analyze --flutter-repo) does not report any problems on my PR.
• I am willing to follow-up on review comments in a timely manner.

Breaking Change

Did any tests fail when you ran them? Please read Handling breaking changes.

• Yes, this is a breaking change.
  • I wrote a design doc: https://flutter.dev/go/annotator-tree
  • I got input from the developer relations team, specifically from: Replace with the names of who gave advice
  • I wrote a migration guide: Replace with a link to your migration guide

[dkwingsmt]

Close it for now until the comments for the design review has been resolved.