[Clang] Implement CWG 3043 (support for lifetime extension in enumerating expansion statements)

From my testing, this will end up being quite a bit of code because we need to apply lifetime extension individually to each ‘subexpression’ in the _expansion-initializer_. See https://github.com/llvm/llvm-project/pull/169680#issuecomment-4093665027 for more information.