argThat(...) doesn't work in stricter strong mode about mockito

[matanlurey]

@TedSander tried to type this ArgMatcher internally - there are some tests that still use Dart 1.x semantics internally that fail with this change, but it looks like Dart 2.x works fine. We'll hold off on changing this for a little bit.

[TedSander]

Note this also applies to any, captureThat, and captureAny. Possibly some others.

[TedSander]

So currently this breaks about 8% of tests using mockito internally. We would need to clean that up first.

[srawlins]

I do intend to make Mockito a 2.0-semantics-only package soon, so that typed() is @deprecated and a no-op, and any and argThat do what typed does today. I'll send a PR this week maybe...

We'll have some cleanup because the new semantics will not allow null next to any any argThat arguments, which is a restriction on typed right now. (i.e. It's a breaking change.)

[srawlins]

OK these signatures have changed, and all the any|argThat|captureAny|anyNamed|... API is typed to return Null. I've played around with --no-implicit-casts and --no-implicit-dynamic, and I think Mockito's API should play well.