bug#47363: font locking variable values in Help buffer

[scame]

When inspecting large list values of variables in the Help buffer,
it would make interpreting the list easier if the value had
elisp font lock.

E.g

...
      (cond
       ((eq type 'var)
        font-lock-variable-name-face)
       ((eq type 'type)
        font-lock-type-face)
       ((or
         (not
          (match-string 2))
         (and
          (match-string 2)
          (match-string 4)))
        font-lock-function-name-face)))
    nil t))
  ("^;;;###\\([-a-z]*autoload\\)" 1 font-lock-warning-face prepend)
  ("\\[\\(\\^\\)" 1 font-lock-negation-char-face prepend)
  
("(\\(cl-\\(?:assert\\|check-type\\)\\|error\\|signal\\|user-error\\|warn\\)\\_>"
   (1 font-lock-warning-face))
  (lisp--el-match-keyword . 1)
  ("(\\(catch\\|throw\\|featurep\\|provide\\|require\\)\\_>[    
']*\\(\\(?:\\sw\\|\\s_\\|\\\\.\\)+\\)?"
   (1 font-lock-keyword-face)
   (2 font-lock-constant-face nil t))
  ("\\\\\\\\\\[\\(\\(?:\\sw\\|\\s_\\|\\\\.\\)+\\)\\]"
   (1 font-lock-constant-face prepend))
  ("\\(\\\\\\)\\([^\"\\]\\)"
   (1
    (elisp--font-lock-backslash)
    prepend))
  ("[`‘]\\(\\(?:\\sw\\|\\s_\\|\\\\.\\)\\(?:\\sw\\|\\s_\\|\\\\.\\)+\\)['’]"
   (1 font-lock-constant-face prepend))
  ("\\_<:\\(?:\\sw\\|\\s_\\|\\\\.\\)+\\_>"
   (0 font-lock-builtin-face))
  ("\\_<\\&\\(?:\\sw\\|\\s_\\|\\\\.\\)+\\_>" . font-lock-type-face)
...