getMDKindID/getMDKindNames methods to LLVMContext (and add
convenience methods to Module), eliminating MetadataContext.
Move the state that it maintains out to LLVMContext.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@92259 91177308-0d34-0410-b5e6-96231b3b80d8