ObjectiveC migrator: start migrating to
instancetype methods.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@187004 91177308-0d34-0410-b5e6-96231b3b80d8
ObjectiveC migration: more migration to
instancetype of NSDictionary methods.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@187008 91177308-0d34-0410-b5e6-96231b3b80d8