There have been some more additional reports of a missing 'package:characters' import after upgrading flutter, as well as problems with detecting the correct language version. This has me concerned that our pub caching logic is incorrect. Instead of the tool attempting to guess when pub should be run, always delegate to pub.

This reverts commit 2462f696.

Migrate framework tests for rendering, semantics, widgets to null safety.

* Add transformAlignment and clipBehavior to AnimatedContainer, make Container.transformAlignment an AlignmentGeometry.

* Add clipBehavior test

* Fix comment

* Clarify clipBehavior animation

Woops, this is breaking Dart's golem benchmarks

Split from #66776

Even if pub does not change the packge_config contents, it will still update a timestamp in one of the fields. This causes unnecessary rebuilds. To fix this, generate an additional file when running pub get that only contains the relevant fields and then update the KernelSnapshot rule to depend on it only.

* [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.

When the developer doesn't have permission to create symlinks, we
display specific instructions, but they were only correct for recent
versions of Windows 10. This improves them by:
- Giving the correct instructions for older versions.
- For recent versions, adds a command that will deep-link into the
  settings application so that developers don't have to figure out
  where/how to enable developer mode.

Fixes https://github.com/flutter/flutter/issues/66973

Use the new single `src/platform.dart` import to pick up what is needed
to implement a test platform from both `test_api` and `test_core`.

* migrate material to nullsafety

* address review comments

* address review comments

* fix build