(provided-mode-derived-p): Fix alias case

(provided-mode-derived-p): Fix alias case

The new handling of aliases in `provided-mode-derived-p`
introduced in Emacs-28.1 caused a regression where
(provided-mode-derived-p MODE MODE) returns nil if MODE is an alias.
Rework the loop so we consider an alias as a kind of parent.

* lisp/subr.el (provided-mode-derived-p): Step over aliases separately.

* test/lisp/subr-tests.el (subr-tests--derived-mode-1)
(subr-tests--derived-mode-2): Move out of `provided-mode-derived-p`
and give them properly namespaced names.
(provided-mode-derived-p): Add more tests for aliases.