bug#48307: Feature request: provide default keybindings to change the font size in all windows

[Gregory Heytings]

> Looks good!  A small stylistic comment:
>
> +           (pcase key
> +              ((or ?+ ?=) (* increment 5))
> +              (?- (* (- increment) 5))
> +              (?0 (- global-text-scale-adjust--default-height
> +                     (face-attribute 'default :height)))
> +              (_ (* increment 5)))))
>
> Do you need the first branch?  If you remove it, those cases will be 
> caught by the default fall-through.

Oh yes, indeed!  Thanks :-)