swift234

SE-0025: Allow public members inside internal types. (#3404)

(and any other member with higher access control than its enclosing type)

There's no effect, but it is now considered legal and the compiler will
no longer warn about it. This allows an API author to prototype their
API with proper access levels and still limit the top-level type.

If the new getEffectiveAccess computation turns out to be expensive, we
can cache the result.

Note that the compiler will still warn when putting a public member
inside an extension explicitly marked internal, because the extended
type could be public and then including a public member would be valid.
It is also still an error to put a public member inside a constrained
extension of an internal type, though I think this one is safe to
relax later.

Progress on SE-0025 ('private' and 'fileprivate')