Adds optional scroll interpolation/animation in #8335 via the
good-scroll package. Command support is light right now, but I plan to
expand on it later, and I welcome PRs to do so in the meantime.
Ref: #8335
Normally, this would be too small to warrant its own module, but smooth
scrolling is one of those things that can tip large swaths of
fence-sitting beginners into Emacs' camp. I can't help but imagine how
many people get their impression that Emacs is "laggy" or "slow" solely
from the way it scrolls.
Don't get me wrong, there *are* good reasons to call Emacs slow, but
startup and scrolling speed are not it, yet they are easily overblown
because it's the first thing you see. I might even consider enabling
this by default, but I'll make that decision later.
Fix: #8335
