Adds safe areas around:
1. The body of the colour swatch view (tab 1)
2. The chat header (tab 2)
3. The chat bubbles (tab 2)
4. The 'Sign In' launcher button (tab 3)

Rather than use a Center widget, center the title using AppBar's
centerTitle property. This ensures the title is horizontally centred
with respect to the screen rather than centred in the space between the
leading and trailing app bar widgets, which are asymmetrical in Shrine.

Applies top, left, right media padding for iOS safe area insets. This is
a follow-up to the media padding applied to large titles in
flutter/flutter#13550.

Fixes https://github.com/flutter/flutter/issues/10695

* flutter update-packages

* update plugin registrant for flutter_gallery

* Update plugin test template.

* Add flutter test run verification.

* Tweak and test runs for package projects.

* Revert "Revert engine (#13547)"

This reverts commit ee65db11.

* Keep flaky mark

This reverts commit 05d6b08f.

* partial

* add doc and warning

* add correction

* review

* fix test

* Add more checks to scheduleWarmUpFrame

* review

* add test

Applies media padding (e.g. iOS safe area insets) around the list tile
children inside the InkWell.

Also adds safe area around gallery section titles for consistency with
surrounding list tiles.

Applies left and right media padding to Cupertino navigation bar large
titles.

* Query selection rectangles for all three characters in the text
* Change the last character to be non-whitespace.  Minikin's line breaker will
  truncate whitespace characters at the end of a line.

* add mediaquery docs

* review

We've added a bunch of non-animatable properties to DefaultTextStyle.
This adds them to AnimatedDefaultTextStyle so that you can use them
even when your text style is animating.

* Revert "Include a directory with Flutter assets (#12944)"

This reverts commit 3af6b9cb.

* Revert "Upgrade project.pbxproj to include flutter_assets (#13011)"

This reverts commit 08128cb2.

* Revert "Upgrade complex_layout project.pbxproj to include flutter_assets (#13544)"

This reverts commit 35f1a041.

* mark complex_layout_ios__start_up as flaky

* update APK path in devicelab tests

* add missing transitive dependency on archive

* use path used by flutter tools

**This PR contains a breaking API change:**
`SemanticsConfiguration.addAction()` has been removed and replaces by action-specific setters (`onTap`, `onLongPress`, etc.) to take care of the fact that some action handlers (those, who take arguments) have different signatures.

Increase coverage collection timeout to 2 minutes. Leafy is hitting the limits of the previous timeout of 30 seconds for tests that touch a lot of code in the app. (#13527)

Add more tests, fix docs, fix painting bugs...

Fixes https://github.com/flutter/flutter/issues/12902

Add test for interim state of the animation to make sure we are transitioning the border color the right way. (#13499)

Includes:
flutter/engine#4425

Updating SDK and package versions now that alpha has been rolled to 0.0.20