Command for global adjustments to the default face

Command for global adjustments to the default face

* lisp/face-remap.el (global-text-scale-adjust): New command.
(text-scale-adjust): Refer to the new related command.
(global-text-scale-adjust-resizes-frames): New user option.

* lisp/mwheel.el (mouse-wheel-scroll-amount): Add the new command
to the mouse wheel scrolling events.
(mouse-wheel-global-text-scale): New function.
(mouse-wheel-mode): Use the new function with mouse-wheel-mode.

* doc/emacs/display.texi (Text Scale): Document the new command and
the new user option.

* etc/NEWS: Mention the new command and its bindings, and the new
user option.