[Format/ObjC] Support NS_ERROR_ENUM in ObjC language guesser

Apple added a new NS_ERROR_ENUM macro to help define enums for
NSError codes.

This updates libformat's Objective-C language-guessing heuristic
to detect the new macro as well as related NSError types.

Tested: New tests added.

Reviewed By: MyDeveloperDay

Differential Revision: https://reviews.llvm.org/D147577