* Revert "Revert "Improve performance of collectAllElements (#68065)" (#68207)"

This reverts commit 46ff57d6.

* use fewer elements for benchmark

This reverts commit 8ba5732c.

Fake has been moved from mockito to test to facilitate NNBD, re-export this from flutter_test

This reverts commit d4112424.

* [flutter_test] handle breaking change to test main . Fixes #67382

Reland: #67155

Fixes analysis error caused by landing of material migration, and g3 error caused by moving of fuchsia lib.

This reverts commit e826442e.

Ensures all of the libraries that the application side code import are migrated to null safety. full null safety migration is blocked by json rpc 2 and a breaking change to vm service client.

* migrate material to nullsafety

* address review comments

* address review comments

* fix build

move resampler to handlePointerEvent and fix complex_layout_android__scroll_smoothness with PointerEvent (#66745)

* 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.

* apply upcoming lint cast_nullable_to_non_nullable

* make RenderObjectElement.renderObject non-nullable

Updates all null safe dependencies to versions that allow 2.10 stable and 2.11 dev releases.

Also updates flutter_goldens and flutter_goldens_client to allow 2.11 dev.

Remove fake image implementations, add createTestImage to flutter_test

[versions] update to latest source span and roll engine to  4b8477d11573d233e6791204191c0090f733b05d (#66136)

Expose GestureBinding.handlePointerEvent, replacing dispatchEvent as the preferred way to dispatch events (#64846)

Fix the `character` field of the `RawKeyEvent` to hold correct data on non-Android platforms. (#65667)

This fixes a problem where the character field of the RawKeyEvent was not being set at all for non-Android platforms.

I also updated the key maps, and corrected a problem with the Windows key map where the backquote character wasn't correctly mapped.

This change disables a failing test prevent PR #20385 from merging.

This reverts commit df833986.