[Macros] Requestify member attribute macro expansion directly.
Having a request for semantic declaration attributes while still allowing
the original linked list to be mutated directly can cause use-after-frees
on pointers to old decl attributes. For now, introduce a request that
expands member attribute macros with a side effect of adding the new
attributes to the list. We can revisit this once attribute mutation via
getAttrs() is audited across the frontend.
