Move the ObjC class name stability check logic to the Swift runtime, exposing it as a new SPI called _swift_isObjCTypeNameSerializable.
Update the reporting logic. The ObjC names of generic classes are considered stable now, but private classes and classes defined in function bodies or other anonymous contexts are unstable by design.
On the overlay side, rewrite the check’s implementation in Swift and considerably simplify it.
rdar://57809977
This function checks if a mangled class name is going to be written into an NSArchive.
If yes, a warning should be printed and the return value should indicate that.
TODO: print the actual warning
rdar://problem/32414508
