Move context-menu selection items Defun/List/Symbol to prog-mode (bug#9054)

Move context-menu selection items Defun/List/Symbol to prog-mode (bug#9054)

* lisp/mouse.el (context-menu-functions):
Add context-menu-middle-separator to choices.
(context-menu-region): Move Defun/List/Symbol selection items
to prog-context-menu.

* lisp/progmodes/prog-mode.el (prog-context-menu):
Move Defun/List/Symbol selection items from context-menu-region.
Include text-mode select menu only in strings and comments.

* lisp/textmodes/text-mode.el (text-mode-menu): New function.
(text-mode): Add text-mode-menu to context-menu-functions.