* Remove the workaround that pinned args to v0.13.6
This reverts most of the changes in commit 6331b6c8b5d964ec0dbf2cd9bb84c60c650a0878
* throw exception if exit code is not an integer
* rework command infrastructure to throw ToolExit when non-zero exitCode
* convert commands to return Future<Null>
* cleanup remaining commands to use throwToolExit for non-zero exit code
* remove isUnusual exception message
* add type annotations for updated args package
* Update tools to use `analyzer` from vended Dart SDK.
* updates `flutter_tools` and `flutter_test` to use the SDK-vended `analyzer` package
* tweaks dependency tracking logic to only record the SDK-vended `analyzer` so as not to crash on spurious conflicts (due to transitive dependencies)
* Review fixes.
