`@internal` should disable `public_member_api_docs` when applied on variables

[rrousselGit]

Consider:

@internal
int a = 42;

This will trigger the public_member_api_docs lint.

This is inconsistent with @internal applied on classes:

@internal
class A{} // No public_member_api_docs lint
```Ï

[rrousselGit]

The same applies should apply to typedef, constructors, and any other annotated element.

I assume the fix should be as simple as changing visitClassDeclaration to visitAnnotatedNode or something similar :)