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

[Gregory Heytings]

> > > There's something more subtle happening, because using 
> > > text-scale-adjust is much faster, even on a frame with a single 
> > > buffer.
> >
> > Again I don't know, but I don't think so.  AFAICS it's faster because 
> > redisplaying a single buffer without changing the window and frame size 
> > is faster than redisplaying all buffers in a frame and resizing the 
> > frame itself.
>
> Enlarging the frame means we also interact with the WM and await its 
> response, no?

The patch I just sent avoids that problem, and does what other programs do 
when the user zooms: their frames are not resized.