New locale resolution algorithm to use full preferred locale list, include scriptCode in Locale. (#23583)

This reverts commit 71e9bd6f.

This re-lands 3c56e6c7 on top of a new Dart SDK that contains new mixin syntax fixes.

* prefer_void_to_null in flutter_test

* fix CI

This reverts commit 3c56e6c7.

It breaks the AOT build.

* first pass

* revert WidgetsBindingObserver

* disable prefer_mixin

* docs and more mixins

* newer engine; binding fixes

* upgrade dependencies

* fix test binding

* remove whitespace

* remove the obsolete `enableSuperMixins: true`

* upgrade dartdoc to 0.22.0

* temporarily use git version of dartdoc

* fix pub global activate syntax

* use dartdoc 0.23.0

* enable lint unnecessary_new

* fix tests

* fix tests

* fix tests

* 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 For cases where the link was out of date, I updated the link.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

It was causing problems rolling Flutter into Fuchsia

* re-enable lint unnecessary_const

* remove trailling whitespaces

* remove unnecessary const (after merge)

This reverts commit cc1cf13e.

Revert "Revert "Roll engine to fed2ea458ed49088d33eddabc546ba56d600c717 (includes dart roll) again (#19277)" (#19295)" (#19322)

This reverts commit cc122f16.

Revert "Roll engine to fed2ea458ed49088d33eddabc546ba56d600c717 (includes dart roll) again (#19277)" (#19295)

This reverts commit 700cb767 as it
breaks Windows tests.

* Revert "Revert "Roll engine to fed2ea458ed49088d33eddabc546ba56d600c717 (includes dart roll) (#19044)" (#19276)"

This reverts commit cf932490 as it also
includes fix for type error that broke tests.

* Add type cast for dart2 type checks.

* Move up to latest goldens

* Make inDirectory() type-parameterized.

* Add typecasting to transitions_perf_test.dart and microbenchmarks.

* Add boolean flag initialization in save_catalog_screenshots.dart

* Add type conversion to gallery transition test

Revert "Roll engine to fed2ea458ed49088d33eddabc546ba56d600c717 (includes dart roll) (#19044)" (#19276)

This reverts commit f4a038da as it breaks microbenchmark tests.

* Roll engine to rolled dart
Add connectionTimeout property to class that extends HttpOverrides.
Upgrade packages.
Add more type fixes.
Update goldens hash.
Add more type fixes.
Upgrade packages.
Fix tests.
Remove strong-mode from analysis options yaml file.
Increase dev/devicelab timeout from 2 to 10 seconds.
Added getVM to waitForViews. Fix type errors in compileExpression.

* Pick up engine revision with fix for microbenchmarks regression.
Increase default timeout from 20/30 to 60s.

Instead, if the surface is 0x0 semantics will just generate one root semantics node with size of 0x0. The node will have no children because all children are invisible and (except for the root node with this change) invisible children are dropped.

* Roll the engine.

This engine includes a VM that defaults to sync-async.

flutter/engine@c8eeee4 Roll the Dart VM.

This should reduce the number of flakes without actually increasing
the timeout, so we'll still find out quickly if a test is hanging.

The numbers here might need tweaking. Maybe the default two seconds is
too short for CI bots.

Enable --sync-async in Flutter.
Fixes #16801 

This reverts commit 39d7f22a.

This allows test environments other than `flutter test` to have a hook
into the test exception reporting. Some test environments, for example,
don't just dump error details to the console, but rather require them
to be reported to a separate server.

Our style guide says the k's are not necessary, and it seems like a good idea to make all the code be consistent on this.

Only naming changes to private vars: no logic changes.