Move from `test.dart` into new `runner_utils.dart` file:
- shard calculation related methods + `shuffleSeed` logic
- env variable flag calculation
- runner wrapper methods `runDartTest` and `_runFromList`
Create web tests suite class containing:
- web long running tests
- runWebHtmlUnitTests
- runWebCanvasKitUnitTests
- runWebSkwasmUnitTests
- the associate helper methods with the above
Refactor flutter_plugins suite in order to reduce testing logic in test.dart and allow for later implementing package:test onto the existing flutter_plugins tests
Also update the test_test invocation of getFlutterPackagesVersion
Part of https://github.com/flutter/flutter/issues/145482