bug#28182: maybe implement CTRL++ to zoom text

[Juri Linkov]

> One small comment regarding the patch.  We could perhaps get away with
> not adding the defvar mwheel-installed-text-scale-bindings, but I
> added that to make sure that we don't accidentally remove any key
> bindings we didn't mean to.  I might be too defensive here, though, so
> please let me know if simpler code is preferred here over this level
> of cautiousness.

Nice change.  Another variant is to add special symbols to
the existing customization, e.g.:

  '(5 ((shift) . 1) ((control) . text-scale) ((meta) . nil))

or even support text-scale step number if needed:

  '(5 ((shift) . 1) ((control) . (text-scale . 1)) ((meta) . nil))

This is similar to what I proposed with

  '((shift) . (hscroll . 1))

to scroll horizontally like Shift-wheel does in web browsers:

https://lists.gnu.org/archive/html/emacs-devel/2010-10/msg00202.html

Also please look at discussions for other related requests:

https://lists.gnu.org/archive/html/emacs-devel/2015-05/msg00529.html
https://lists.gnu.org/archive/html/emacs-devel/2017-03/msg00797.html
https://lists.gnu.org/archive/html/emacs-devel/2017-09/msg00129.html