Split ObjCInterfaceDecl::ReferencedProtocols into two lists:...

Split ObjCInterfaceDecl::ReferencedProtocols into two lists: ReferencedProtocols and AllReferencedProtocols.  ReferencedProtocols
(and thus protocol_begin(), protocol_end()) now only contains the list of protocols that were directly referenced in
an @interface declaration.  'all_referenced_protocol_[begin,end]()' now returns the set of protocols that were referenced
in both the @interface and class extensions.  The latter is needed for semantic analysis/codegen, while the former is
needed to maintain the lexical information of the original source.

Fixes <rdar://problem/8380046>.

llvm-svn: 112691