Contains the following changes:
4fde39583 Roll Dart to version ccb16f72824374163562364bf19dd18e8a882fab (#6065)
140a5b757 Alllow access to Flutter engine, Dart & Skia versions in the Shell API. (#6060)

* [Gallery] Elevations demo. TODO: Correct icon.

* [Gallery] More elevations for the elevation demo.

* [Gallery] Elevation toggle for elevation demo.

* [Demos] Update temp icon on elevations demo.

* [Demos] Changing action icon.

* [Demos] Same.

* [Demos] Adding new and const.

* [Demos] Reverting formatting.

* [Gallery] PR Feedback.

Tabs are now padded by 16.0 on the left and right  (used to be 12.0).

The team captain wins the arena on behalf of the team.
When any of the team members claims victory for the arena the captain
accepts the gesture.

This is used when embeddeding platform views - we allow configuring a
set of gestures that should be forwarded to the platform view.
We add the set of gesture recognizers to a GestureArenaTeam with a
captain, and if the captain accepts the gesture we forward it to the
platform view.

This fixes #20483 by letting InkWell do its own clipping.

PathOp.intersect is not used because we have too many unit tests that rely on clipping (e.g., paints..clipXXX()..drawCircle())

The goldens are updated due to small AA changes of the additional clipPath.

This test is sometimes flaky (#20822) because the two processes try to stop the same app. This fix changes to just gracefully terminate the attach process without explicitly trying to stop and then uses the original spawning process to stop the app.

I can't repro the flake locally to be certain, but I've verified only one stop command is sent now so it *should* be good.

Due to CPU contention we've seen these go really slow on Cirrus (see https://github.com/flutter/flutter/issues/19542#issuecomment-414265152), and there's also a chance our flakes are timeouts due to running slow rather than hanging.

BottomNavigationBar's state needs to update _backgroundColor when its configuration changes.

- remove an //ignore that is no longer needed
- fix some intrinsic methods that used the API incorrectly (shouldn't affect correctness but should make things a tiny bit more efficient)
- add some asserts to help track down bugs quicker
- update a TODO to point to the currently relevant bug
- fix some indenting
- improve the naming of some privates to improve readability

* Track number of package dependencies in Flutter

Relands #20774.

* Use evalFlutter instead of startProcess.

That way we don't need `flutter` on the PATH.

Fixes the pattern for some TODOs to match our style guide.

(Also, a couple of minor code order fixes.)

Require componentName to ensure assets are placed under /pkg/data/<component-name>

This will be needed once PhysicalShape sets the default clipBehavior
to Clip.none.

* Don't keep parsing results once we've had the event we expected

* Report errors if an app.stop event is received while waiting for another event

* Don't throw if we see app.stop event when we've just sent an app.stop request

* Improve debug print to include --start-paused if being used

* Improve wrapping

* add a --use-cfe option to flutter analyze

* useCFE ==> useCfe

* Add ability to set collapse mode in flexible space bar

* Add tests to collapse mode in flexible space bar

* Fix minor style nit

* Fix getting collapse mode does not handle unknown values

* Change const key to final in space bar collapse mode test

* Return null collapse padding if mode is unknown

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If //ignore is bad, ignoring something for a whole file is presumably worse.

For #20483

The tool was failing if we had 2 separate non-canonical paths to the
same canonical paths.

flutter_tools cannot depend on flutter_goldens (as flutter_goldens
depdends on the Flutter sdk), so this commit splits client.dart from
flutter_goldens to a pure-dart flutter_goldens_client package.

The test places an embedded Android view at the top left, and verifies
that motion events that get to FlutterView are equivalent to the
synthesized motion events that gets to the embedded view.

See the README.md for more high level details.

* `flutter analyze` cleanup

* Make `--dartdocs` work in all modes.
* Make `analyze-sample-code.dart` more resilient.
* Add a test for `analyze-sample-code.dart`.
* Minor cleanup in related code and files.

* Apply review comments

* Fix tests

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* Allow option switches to have keys

* Review comments

Turns out we weren't deleting the dill directory or the fonts directory.

* Fixes resulting from audit of issues links

I looked at every link to GitHub in our repo. For cases where we had a TODO that was waiting for a bug to be fixed, and the bug has now been fixed, I applied the pending change. For cases where the link was out of date, I updated the link.

* Update run_test.dart

skip this test again since it failed on linux and macos bots

* Revert "Deprecated CupertinoDialog in favor of a new widget called CupertinoP… (#20649)"

This reverts commit 3a4ae280.

* Revert "Feature pesto new recipes (#19415)"

This reverts commit e2f3b3d6.

* Revert "Use markdown table (#20721)"

This reverts commit 82d43b95.

* Revert "Documentation regarding tap gesture callbacks (#20647)"

This reverts commit 3acc2785.

* Revert "Add branch to footer information in flutter docs (#20711)"

This reverts commit 9118d3d7.

* Revert "Performance test cleanup (#20652)"

This reverts commit 1993a673.

* Revert "Track number of package dependencies in Flutter (#20722)"

This reverts commit 03d6f18f.

Deprecated CupertinoDialog in favor of a new widget called CupertinoPopupSurface. (#20397)