Add new context menu functions to the context-menu-functions type

* lisp/mouse.el (context-menu-functions): Add new menu functions
to the defcustom type list (bug#52973).

lisp/hi-lock.el

@@ -862,6 +862,7 @@ SPACES-REGEXP is a regexp to substitute spaces in font-lock search."
     (mouse-set-point event)
     (highlight-symbol-at-point)))
 
+;;;###autoload
 (defun hi-lock-context-menu (menu click)
   "Populate MENU with a menu item to highlight symbol at CLICK."
   (save-excursion

lisp/man.el

@@ -1984,6 +1984,7 @@ Uses `Man-name-local-regexp'."
     (mouse-set-point e)
     (man (Man-default-man-entry))))
 
+;;;###autoload
 (defun Man-context-menu (menu click)
   "Populate MENU with commands that open a man page at point."
   (save-excursion

lisp/mouse.el

@@ -298,6 +298,9 @@ and should return the same menu with changes such as added new menu items."
                   (function-item context-menu-buffers)
                   (function-item context-menu-vc)
                   (function-item context-menu-ffap)
+                  (function-item Man-context-menu)
+                  (function-item hi-lock-context-menu)
+                  (function-item context-menu-online-search)
                   (function :tag "Custom function")))
   :version "28.1")