Add `MDTupleTypedArrayWrapper`, a wrapper around `MDTuple` that adapts
it to look like an array and cast its operands to the given type. This
is designed to be a replacement for `DITypedArray<>`, which is in the
`DIDescriptor` hierarchy.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@234183 91177308-0d34-0410-b5e6-96231b3b80d8