bug#63187: 30.0.50; Tail of longer lines painted after end of nearby lines on macOS

[Eli Zaretskii]

> From: Aaron Jensen <aaronjensen@gmail.com>
> Date: Sun, 30 Apr 2023 10:57:35 -0400
> Cc: luangruo@yahoo.com, 63187@debbugs.gnu.org
> 
> For what it's worth, disabling it has had no discernible impact on
> scroll performance on my machine (which is an M1)

scrolling_window is not about scrolling.  It's a redisplay
optimization that attempts to speed up redrawing a window by scrolling
on display the stuff already shown, when that is deemed less costly
than redrawing every screen line that has changed.