[NFC] Refactoring PropertyAttributeKind for ObjCPropertyDecl and ObjCDeclSpec.

This is a code clean up of the PropertyAttributeKind and
ObjCPropertyAttributeKind enums in ObjCPropertyDecl and ObjCDeclSpec that are
exactly identical. This non-functional change consolidates these enums
into one. The changes are to many files across clang (and comments in LLVM) so
that everything refers to the new consolidated enum in DeclObjCCommon.h.

Differential Revision: https://reviews.llvm.org/D77233