Add matchers for testing the stacktrace when an object is thrown

[rrousselGit]

Hello!

When dealing with error handling, it's quite important to make sure that the proper stacktrace is passed around. But at the moment, we don't really have a matcher to test the stacktrace when an error is thrown.

I think it would be helpful if we had a way to simultaneously both check the error thrown and the stacktrace. For this, I think an optional parameter on throwsA would be helpful.

We would be able to write:

Matcher throwA(Object errorMatcher, [Object? stackTraceMatcher]); 

await expectLater(
  Future<int>.error(StateError(''), StackTrace.empty),
  throwsA(isStateError, equals(StackTrace.empty)),
);