isInstanceOf should be a method

[Hixie]

@kevmoo @natebosch
Based on our meeting today, Flutter is hiding TypeMatcher and isInstanceOf from test in all our tests (and in the flutter_test package that we export to our users), and instead just exporting a function called isInstanceOf. This is ugly and we would prefer if we could just have an isInstanceOf method so that we didn't need to have these hacks.

[kevmoo]

When we're ready to roll a major release of matcher + test, we'll make this change!

[Hixie]

dart-archive/matcher#110 didn't solve this. It used a different name that won't allow us to unfork.

[natebosch]

Will leave open until we can remove isInstanceOf with a breaking change version bump.

[natebosch]

Discussed offline - flutter_test will keep it's own isInstanceOf unless they decide to do a breaking change, or forever, which can be handled independently from anything test. We will not keep isInstanceOf in matcher or test once we have other compelling reasons for a breaking version bump.

[jamesderlin]

I'm not sure what the current intention is, but currently the documentation for isInstanceOf says:

DEPRECATED Use TypeMatcher instead.

but also:

Annotations
@deprecated('Use isA<MyType>() instead.')

which seems inconsistent.

[jamesderlin]

It's also confusing to recommend using TypeMatcher because Flutter has its own copy of the package:matcher docs, but in a Flutter context, package:matcher's TypeMatcher is hidden and TypeMatcher is something different.