Generate warnings on unnecessary package access methods and fields in views

[realityforge]

A few bugs have been identified as a result of other objects invoking methods on @View annotated methods. We could generate warnings if a @View declares a package access method or package-access field where it is not necessary for it to be package access. Essentially this would involve generating warnings for package-access methods and fields unless they are annotated with either an arez annotation or a react4j annotation.

This warnings should be suppress-able just in case there is a valid reason that we have yet to think of

[realityforge]

We should also generate a warning if any non-private class is enclosed within the @View annotated type.