bug#39901: Emacs needs to update window-width when the user updates the text size

[Drew Adams <drew.adams@oracle.com>]

> Emacs needs to update window-width when
> the user updates the text size.

Apologies for not following this thread,
and if this reply is off-topic.  I stumbled
on this message by chance.

FWIW, letting users automatically resize
the window to accommodate a change in
text scale is the purpose of library
`face-remap+.el'.  This enhancement was
proposed to Emacs dev from the outset
(2009), but there was no interest.

`face-remap+.el' lets buffer font
resizing also zoom the window size
accordingly (horizontally, vertically,
or both).  That way, you can take
advantage of the space freed up by
resizing (text-scaling) to a smaller
font.

The code has just a small change to
`text-scale-increase'.

https://www.emacswiki.org/emacs/download/face-remap%2b.el

Option `text-scale-resize-window'
lets you control the behavior:

nil:            Don't resize window
`horizontally': Resize window only horizontally
`vertically':   Resize window only vertically
t:              Resize window both directions

[If the window is alone in its frame, and if
you also use library `fit-frame.el', then the
frame is resized (horizontally & vertically).]