*  Add IgnorePointer Widget dartpad

*  Fix grammatical issues in docs of IgnorePointer

*  Remove trailing spaces

* Fix crash when widgetspan does not produce a semantics node in render paragraph

* fix comments

* fixed corner case, added test, refactored semantics widget

* addressing comment

* Add a code sample for the [Offstage] widget

My yearly pass to fix spelling errors in the API dartdocs.

Reland "Add CompositedTransformFollower.{followerAnchor, leaderAnchor} for custom anchoring (#64930)" (#65871) (#65884)

* Reland dispose images when done (#67100)

Changes since last time:

- Test for CanvasKit image rendering
  (https://github.com/flutter/flutter/pull/67176)
- Fix CanvasKit dispose impl
  (https://github.com/flutter/engine/pull/21555)
- Update internal google3 customer with a problematic ImageStream
  Listener impl (cl/335091311, cl/335459002)

This reverts commit 473358d9.

* Revert "docs for image disposal (#67066)"

This reverts commit bcb2ac5a.

* Revert "Dispose of images after using them (#66688)"

This reverts commit a7954691.

* Dispose of images after using them
Adds ImageInfo.clone, ImageInfo.dispose, and ImageInfo.isCloneOf.
Makes all stateful holders of ui.Image objects properly clone and dispose of them.
Behavior change for ImageStreamCompleter: Removing the last listener after registering at least one listener results in the object being disposed, and new listeners cannot be added, unless a keepAlive handle is created.
Makes all non-stateful holders of ui.Image (i.e. paintImage and RawImage) assert that whoever gave the image to them has not disposed it on them.

This is a continuation of https://github.com/flutter/flutter/pull/61366
after cl/333620714

See also https://flutter.dev/go/clip-behavior

* apply upcoming lint cast_nullable_to_non_nullable

* make RenderObjectElement.renderObject non-nullable

Revert "Add CompositedTransformFollower.{followerAnchor, leaderAnchor} for custom anchoring (#64930)" (#65871)

This reverts commit 2fbb529d.

This follows https://github.com/flutter/flutter/pull/59364 and cl/319911104

FittedBox is still default to hardEdge clip as new FittedBox is added to Google very quickly. Let's first roll other part of changes into Google first.

* Reland "Nnbd widgets (#64672)"

This reverts commit 127e6790.

* remove non-nullable enforcement on AsyncSnapshot

* make data param non-nullable for AsyncSnapshot.withData

* make some Text params non-nullable