Fix #'fun handling inside `labels' (Bug#31792)

Fix #'fun handling inside `labels' (Bug#31792)

* lisp/emacs-lisp/cl.el (labels): Apply the equivalent of the
cl-labels change from 2015-01-16 "* lisp/emacs-lisp/cl-macs.el: Fix
last change".
* test/lisp/emacs-lisp/cl-tests.el (labels-function-quoting): New
test.
* lisp/emacs-lisp/cl-macs.el (cl-flet, cl-labels): Improve docstring,
link to relevant manual page.
* doc/misc/cl.texi (Function Bindings): Don't imply that function
cells of symbols are modified by cl-flet.  Don't claim that cl-flet or
cl-labels affect references of the form (quote FUNC).