Address review feedback on r221933.

Remove ObjCMethodList::Count, instead store a "has more than one decl" bit in
the low bit of the ObjCMethodDecl pointer, using a PointerIntPair.

Most of this patch is replacing ".Method" with ".getMethod()".

No intended behavior change.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@224876 91177308-0d34-0410-b5e6-96231b3b80d8