[objcarcopts] Encapsulate PtrState.RRI.ReleaseMetadata into the methods PtrState.GetReleaseMetadata() and PtrState.SetReleaseMetadata().

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@184534 91177308-0d34-0410-b5e6-96231b3b80d8