[rfw] Remote Flutter Widgets package (flutter#452)

[pigeon] fixed cases where types can be missing from codecs (flutter#468

)

[extension_google_sign_in_as_googleapis_auth]updated the code snippet (…

…flutter#463)

[cross_file] Unify XFile interface on web and mobile (flutter#459)

This change changes a couple of methods in the specific implementations of XFile so they implement better the API defined in XFileBase (proper getters instead of public read-only properties)

[pigeon] made it so async java handlers can report errors (flutter#460)

[pigeon] fixed bug where classes aren't generated (flutter#458)

fixed bug where classes aren't generated when they are only referenced as type arguments.

Test that IPv6 sockets get closed (fe5dc35) (flutter#457)

[pigeon] updated to 1.0.0 (flutter#447)

[palette_generator] Add PaletteGenerator.fromByteData (flutter#450)

[flutter_markdown]: Release v0.6.6 (flutter#453)