Add infrastructure to apply a derive macro to arguments, consuming and
returning a `TokenTree` only.
Handle `SyntaxExtensionKind::MacroRules` when expanding a derive, if the
macro's kinds support derive.
Add tests covering various cases of `macro_rules` derives.
Note that due to a pre-existing FIXME in `expand.rs`, derives are
re-queued and some errors get emitted twice. Duplicate diagnostic
suppression makes them not visible, but the FIXME should still get
fixed.
