Allow any to work with Strong mode

[srawlins]

This is a sibling issue to dart-lang/sdk#26036.

The issue is that we cannot use any with Strong mode turned on. For example:

int f(List<int> l) => l[0];

void main() {
  f(any);
}

Yields an analyzer error (dartanalyzer --strong a.dart): "Unsound implicit cast from dynamic to List".

I think we can solve this on the Mockito side, similar to Java Mockito's any().

I have a prototype implementation that uses the Strong mode type parameter comments:

/*=T*/ any/*<T>*/([/*=T*/ e = null]) => null;

The tricky part is that any would now return null, instead of the _ArgMatcher (again similar to Java Mockito's, and we would have to implement something like Java Mockito's reportMatcher(), maybe changing how the whole matching situation works...

What do you think? Any thoughts or other ideas?

[leafpetersen]

@kevmoo Any thoughts on this?