Migrate yet even more widget framework tests to null safety.

This reverts commit d962c8f2.

This crash affects anyone using flutter, so move it into the tool where it can be tested and documented. Ensure it works on windows devicelab too.

This reverts commit 6aa8447a.

This reverts commit 8ba5732c.

* NNBD widget test migration

These androidx migration tests require downloading firebase, which is a large library with a number of dependencies - this causes frequent enough flakes.

AndroidX migration is ~2 years in the past, and while it would be nice to confirm this still works, ideally that would be done in a reduced manner.

* [flutter_tools] partial revert of start app change

- run_without_leak_tests: have been disabled for months
- build_benchmark: the tooling work here is mostly done and we're not tracking further improvements, free up more devicelab capacity
- system_debug_ios: does not work post iOS13
- mac_enable_twc: not adding more mac tests to devicelab
- hello_world_start_up: disabled

Any tests that we think will be valuable in the future can be resurrected from the git history.

Revert "[flutter_tools] If run fails to install the application on iOS, try uninstalling it and trying again. (#68078)" (#68118)

This reverts commit 61ba7dd2.

[flutter_tools] If run fails to install the application on iOS, try uninstalling it and trying again. (#68078)

[Material] Parent checkbox in DataTable should deselect all, if children checkboxes are disabled or selected  (#67938)

* modify: add prefix `Alignment.` for toString of Alignment

Do not allow attach in release mode, as there is not VM Service to connect to. Observed in crash reporting as thrown string which is changed to exception below.