ObjectiveC: Refactor applyObjCProtocolQualifiers.

To construct the canonical type of ObjCTypeParamType, we need to apply
qualifiers on ObjCObjectPointerType. The updated applyObjCProtocolQualifiers
handles this case by merging the protocol lists, constructing a new
ObjCObjectType, then a new ObjCObjectPointerType.

rdar://24619481
rdar://25060179

Differential Revision: http://reviews.llvm.org/D24059

llvm-svn: 281353