contains() should auto-wrap in a matcher

[tvolkert]

Use case:

expect(fontManifest, contains({
  'family': 'DummyFont',
  'fonts': [
    {'asset': 'fonts/dummy_font_regular'},
    {'asset': 'fonts/dummy_font_bold', 'weight': 600},
    {'asset': 'fonts/dummy_font_italic', 'style': 'italic'},
    {'asset': 'fonts/dummy_font_bold_italic', 'weight': 600, 'style': 'italic'},
  ],
}));

Right now, this doesn't work, and the user has to explicitly call wrapMatcher() to get the desired behavior:

expect(fontManifest, contains(wrapMatcher({
  'family': 'DummyFont',
  'fonts': [
    {'asset': 'fonts/dummy_font_regular'},
    {'asset': 'fonts/dummy_font_bold', 'weight': 600},
    {'asset': 'fonts/dummy_font_italic', 'style': 'italic'},
    {'asset': 'fonts/dummy_font_bold_italic', 'weight': 600, 'style': 'italic'},
  ],
})));

It'd be more elegant if contains() implicitly called wrapMatcher() if it were matching against a non-string value.

[tvolkert]

/cc @nex3

[nex3]

I believe the reason this doesn't work currently is that contains() is also used to check if a string contains a substring, where wrapping doesn't make sense. But we should be able to call wrapMatcher() on the argument at match-time if the actual value is a collection.

This would technically be a breaking change... we should do it as part of the 1.0.0 refactor.