Preserve arg names for advice of subr and lexical functions.

Preserve arg names for advice of subr and lexical functions.
* lisp/help-fns.el (help-function-arglist): Consolidate the subr and
new-byte-code cases.  Add argument `preserve-names' to extract names
from the docstring when needed.
* lisp/emacs-lisp/advice.el (ad-define-subr-args, ad-undefine-subr-args)
(ad-subr-args-defined-p, ad-get-subr-args, ad-subr-arglist): Remove.
(ad-arglist): Use help-function-arglist's new arg.
(ad-definition-type): Use cond.

Fixes: debbugs:8457