Support testing expectations on StackTraces for thrown exceptions #2706

The .throws() expectation on both Function() and Future subjects allows checking further details about the thrown object, but does not expose the stack trace at all for testing. This is also what matcher supports, and testing expectations on stack traces is rare.

If we had only the Condition (or as a class or callback) style arguments we could add a second optional argument for a condition to check the stack trace, but this design doesn't work as well with the model where we return a Subject or Future<Subject>.

We could use Subject<({Object error, StackTrace stackTrace})>, but this would require reading the error getter for each use.