ObjectiveC generics: Add ObjCTypeParamType in the type system.

We also need to add ObjCTypeParamTypeLoc. ObjCTypeParamType supports the
representation of "T <protocol>" where T is a type parameter. Before this,
we use TypedefType to represent the type parameter for ObjC.

ObjCTypeParamType has "ObjCTypeParamDecl *OTPDecl" and it extends from
ObjCProtocolQualifiers. It is a non-canonical type and is canonicalized
to the underlying type with the protocol qualifiers.

rdar://24619481
rdar://25060179

Differential Revision: http://reviews.llvm.org/D23079

llvm-svn: 281355