Purpose uncertain. I guess it's slightly better, maybe.
The move of the sws/zimg options from VO opts (vo_opt_list) to the
top-level option list is tricky. VO opts have some helper code in vo.c,
that sends VOCTRL_SET_PANSCAN to the VO on every VO opts change. That's
because updating certain VO options used to be this way (and not just
the panscan option). This isn't needed anymore for sws/zimg options, so
explicitly move them away.
mp_sws_set_from_cmdline() has the only purpose to respect the --sws-
command line options. Instead of forcing callers to get the option
struct containing these, let callers pass mpv_global, and get it from
the option core code directly. This avoids minor annoyances later on.