Ignore parens in strings for outline headings in emacs-lisp-mode.

Ignore parens in strings for outline headings in emacs-lisp-mode.

* lisp/outline.el (outline-font-lock-keywords): For non-nil
outline-search-function return a lambda that calls the function,
then sets the match data to the end of the line that is equivalent
to adding ".*" in the regexp.  Then search functions don't need to
match ".*" themselves.

* lisp/progmodes/elisp-mode.el (elisp-outline-search):
New function to skip leading parens in strings when searching
for outline headings.
(emacs-lisp-mode): Set buffer-local 'outline-search-function' to
'elisp-outline-search'.
https://lists.gnu.org/archive/html/emacs-devel/2025-04/msg00934.html

(cherry picked from commit 746a3cb3143194436c4a1a63d26aac890c1a705f)