bug#47860: 28.0.50; Mini buffer resize when lines are truncated regression

[Eli Zaretskii <eliz@gnu.org>]

> From: Aaron Jensen <aaronjensen@gmail.com>
> Date: Mon, 19 Apr 2021 11:19:06 -0500
> Cc: Gregory Heytings <gregory@heytings.org>, 47860@debbugs.gnu.org
> 
> Okay, here's a selectrum-free repro that, on emacs 27 shows all 3
> lines and on emacs 28 shows only two lines:
> 
> (defun foo--set-window-height (window &optional height)
>   (let ((dheight (or height (cdr (window-text-pixel-size window))))
>         (wheight (window-pixel-height window))
>         (window-resize-pixelwise t))
>     (window-resize
>      window (- dheight wheight) nil nil 'pixelwise)))

Yes, that's the problem: selectrum doesn't rely on the automatic
mini-window resize, it resizes the mini-window manually!  And it
relies on window-text-pixel-size to tell how high should the
mini-window become.

So the root cause is in window-text-pixel-size when this crazy mix of
overlays is used.  Will take a look when I have time.