nadvice.el: Restore interactive-form handling

nadvice.el: Restore interactive-form handling

* test/lisp/emacs-lisp/nadvice-tests.el
(advice-test-call-interactively): Prefer a locally scoped function.

* lisp/simple.el (interactive-form): Don't skip the method dispatch
when recursing.
(interactive-form) <advice>: New method.

* lisp/emacs-lisp/nadvice.el (advice--where-alist): Fix typo.
(advice--get-interactive-form): New function.

* lisp/emacs-lisp/oclosure.el (oclosure-lambda): Fix thinko.

* lisp/emacs-lisp/cl-generic.el: Prefill with an OClosure dispatcher.