Make font-lock face variables obsolete

Using these variables as "another mechanism for changing face
appearance" never really worked, since mode authors were free to use the
face instead of the variable (i.e. quoting the symbol).  This means that
when users customized the variables, it would change its appearance only
in some cases, which is a rather surprising interface.

Indeed, it turns out that some modes have not always been consistent,
and mixed using the variable and the face, increasing the confusion even
further.  Thus, the only thing users could rely on to always work was to
leave the variables at their default value, and to customize the face.

We now recommend customizing the face, and are obsoleting these
variables.  This will lead to some minor code-churn, but it is believed
that it will be ultimately worth it.  To fix existing Lisp code, you
should typically only need to quote the symbol, as this commit shows.

It might be the case that we will have to keep the obsolete variables,
that have been with us since Emacs 19, around for a longer time-period
than normal, to allow package authors to adapt.

* lisp/font-lock.el (font-lock-comment-face)
(font-lock-comment-delimiter-face, font-lock-string-face)
(font-lock-doc-face, font-lock-doc-markup-face, font-lock-keyword-face)
(font-lock-builtin-face, font-lock-function-name-face)
(font-lock-variable-name-face, font-lock-type-face)
(font-lock-constant-face, font-lock-warning-face)
(font-lock-negation-char-face, font-lock-preprocessor-face): Make face
variables obsolete in favor of customizing the faces directly
instead.  (Bug#71469)

* doc/lispref/modes.texi (Faces for Font Lock): Don't document above
obsolete variables.

* lisp/cedet/data-debug.el (data-debug-insert-hash-table)
(data-debug-insert-widget-properties, data-debug-insert-string)
(data-debug-insert-number):
* lisp/emacs-lisp/lisp-mode.el (elisp--font-lock-backslash)
(lisp-font-lock-syntactic-face-function):
* lisp/emacs-lisp/package.el (describe-package-1):
* lisp/generic-x.el (rc-generic-mode, rul-generic-mode):
* lisp/org/org-table.el (org-table-edit-formulas):
* lisp/progmodes/cc-fonts.el (c-font-lock-invalid-single-quotes)
(c-maybe-font-lock-wrong-style-comments, c-font-lock-declarators)
(c-font-lock-c++-lambda-captures, c-font-lock-c++-modules):
* lisp/progmodes/cperl-mode.el (cperl-find-sub-attrs)
(cperl-look-at-leading-count, cperl-process-here-doc)
(cperl-find-pods-heres):
* lisp/progmodes/gdb-mi.el (gdb-init-1, gdb-update, gdb-running)
(gdb-starting, gdb-stopped, gdb-internals)
(gdb-breakpoints--add-breakpoint-row, gdb-locals-handler-custom)
(gdb-registers-handler-custom, gdb-get-source-file):
* lisp/progmodes/js.el (js--font-lock-keywords-1)
(js--font-lock-keywords-2, js-font-lock-syntactic-face-function):
* lisp/progmodes/lua-ts-mode.el (lua-ts--comment-font-lock):
* lisp/progmodes/meta-mode.el (meta-indent-in-string-p):
* lisp/progmodes/prolog.el (prolog-font-lock-keywords):
* lisp/progmodes/python.el (python-font-lock-syntactic-face-function):
* lisp/progmodes/ruby-ts-mode.el (ruby-ts--comment-font-lock):
* lisp/progmodes/sh-script.el (sh-font-lock-syntactic-face-function):
* lisp/textmodes/tex-mode.el (doctex-font-lock-syntactic-face-function):
* test/lisp/faces-tests.el (faces--test-color-at-point):
* test/lisp/progmodes/cperl-mode-tests.el (cperl-test-extra-delimiters)
(cperl-test-bug-47112, cperl-test-bug-65834, cperl-test-bug-66145)
(cperl-test-bug-66161, cperl-test-bug-69604):
* test/lisp/progmodes/python-tests.el
(python-ts-mode-compound-keywords-face)
(python-ts-mode-named-assignment-face-1)
(python-ts-mode-assignment-face-2, python-ts-mode-nested-types-face-1)
(python-ts-mode-union-types-face-1, python-ts-mode-union-types-face-2)
(python-ts-mode-types-face-1, python-ts-mode-types-face-2)
(python-ts-mode-types-face-3, python-ts-mode-isinstance-type-face-1)
(python-ts-mode-isinstance-type-face-2)
(python-ts-mode-isinstance-type-face-3)
(python-ts-mode-superclass-type-face, python-ts-mode-class-patterns-face)
(python-ts-mode-dotted-decorator-face-1)
(python-ts-mode-dotted-decorator-face-2)
(python-ts-mode-builtin-call-face)
(python-ts-mode-interpolation-nested-string)
(python-ts-mode-level-fontification-wo-interpolation)
(python-ts-mode-disabled-string-interpolation)
(python-ts-mode-interpolation-doc-string):
* test/lisp/progmodes/ruby-mode-tests.el
(ruby-heredoc-font-lock, ruby-heredoc-highlights-interpolations)
(ruby-exit!-font-lock, ruby-regexp-interpolation-is-highlighted)
(ruby-recognize-symbols-starting-with-at-character)
(ruby-hash-character-not-interpolation)
(ruby-interpolation-suppresses-quotes-inside)
(ruby-interpolation-suppresses-one-double-quote)
(ruby-interpolation-inside-percent-literal)
(ruby-interpolation-inside-percent-literal-with-paren)
(ruby-interpolation-inside-another-interpolation)
(ruby-interpolation-inside-double-quoted-percent-literals)
(ruby-no-interpolation-in-single-quoted-literals):
Don't use above obsolete variables.
* lisp/progmodes/cc-fonts.el (font-lock-constant-face): Don't
declare now-unused variable.

lisp/emacs-lisp/lisp-mode.el

@@ -308,7 +308,7 @@ This will generate compile-time constants from BINDINGS."
                                 (buffer-substring-no-properties
                                  beg0 end0)))))
                 (buffer-substring-no-properties (1+ beg0) end0))
-         `(face ,font-lock-warning-face
+         '(face font-lock-warning-face
                 help-echo "This \\ has no effect"))))
 
 (defun lisp--match-confusable-symbol-character  (limit)
@@ -660,9 +660,9 @@ Lisp font lock syntactic face function."
           (let ((listbeg (nth 1 state)))
             (if (or (lisp-string-in-doc-position-p listbeg startpos)
                     (lisp-string-after-doc-keyword-p listbeg startpos))
-                font-lock-doc-face
-              font-lock-string-face))))
-    font-lock-comment-face))
+                'font-lock-doc-face
+              'font-lock-string-face))))
+    'font-lock-comment-face))
 
 (defun lisp-adaptive-fill ()
   "Return fill prefix found at point.