docs: simplify format requirements

docs: simplify format requirements

When I initially started writing these lists, I expected the lists to be
much less uniform in what bits were required. Turns out I was wrong, and
this ended up really neat and orderly.

I'm sure we're missing some defacto requirements here and there,
especially for the early versions. This list is based on what we check
for in version.c, and it's better than nothing.

Suggested by Mike Blumenkrantz.

Reviewed-By: Mike Blumenkrantz <michael.blumenkrantz@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/9602>