Flutter `emulator launch` crash running in dart-2-mode (#19454)

* Only printError on our simple messages

Any other type is a real error that should be a normal crash (to get a proper error log).

See #19453.

* Add toList() to convert Iterable<String> -> List<String>

This code previously throw in Dart-2 mode.

Fixes #19453.

* Move getSimulatorPath into Xcode

* Add a test that we tried to launch the simulator

* Remove unused import