Improve hover scopes for Objective-C code

- Instead of `AppDelegate::application:didFinishLaunchingWithOptions:` you
will now see `-[AppDelegate application:didFinishLaunchingWithOptions:]`

- Also include categories in the name when printing the scopes, e.g. `Class(Category)` and `-[Class(Category) method]`

Differential Revision: https://reviews.llvm.org/D68590