bug#57970: 29.0.50; Create new defgroup for pixel-scroll.el

[Po Lu via "Bug reports for GNU Emacs, the Swiss army knife of text editors" <bug-gnu-emacs@gnu.org>]

Eli Zaretskii <eliz@gnu.org> writes:

> It sounds like your comments actually agree with my suggestions ;-)
>
> To clarify, I didn't mean that pixel-scroll-precision-mode _cannot_ be
> used with wheels, I just said pixel-scroll-mode is _better_ there
> (because it requires no tricky configuration); conversely, for
> touchpads, pixel-scroll-precision-mode produces a much better UX OOTB.

That is correct, but not from an objective standpoint, only from the POV
of what is better "out of the box".  p-s-p-m is worse off OOTB, because
it takes no effect at all without some configuration.

> This particular discussion is about two modes that have very similar
> names.  I think explaining the strengths and weaknesses (even if they
> are minor and can be overcome, given enough efforts) goes at least
> some way towards resolving user confusion about these two, and
> changing the name, even if not 110% accurate, is even better.

Users customarily search for terms in the vein of "pixel scroll", which
that must still be taken into account: whatever name we select for the
mode should incorporate the word "pixel".

One more data point: within the stream of feature requests that
constitued the impetus for my decision to implement this feature, not a
single request mentioned the word "touchpad", whereas "pixel" and
"precise" abounded.  At least in my recollection.