In another change (#37646), I want to test that a test fails and
prints expected output. I didn't see an existing way to do that, so
I modified `_runFlutterTest` and `runCommand` to allow capturing the
output. Currently capturing and printing output are mutually
exclusive since we don't need both.
Some awkward bits:
* There already exists a `runAndGetStdout` function that is very
similar to `runCommand`, and this change makes the conceptual
distinction more confusing.
* `runFlutterTest` has multiple code paths for different
configurations. I don't understand what the different paths are
for, and I added output checking only along one of them.
* add trailing commas on list/map/parameters
* add trailing commas on Invocation with nb of arg>1
* add commas for widget containing widgets
* add trailing commas if instantiation contains trailing comma
* revert bad change
* Split analysis steps out of dev/bots/test.dart into dev/bots/analyze.dart.
This allows to run analysis step with command line arguments that are only applicable to flutter analyze(like --dart-sdk, needed for dart-flutter-engine head-head-head bot).
* Add forgotten dev/bots/analyze.dart
* Refactor common code from analyze.dart and test.dart into run_command.dart
* Remove comments, add header
