previously descriptor buffers were sized to allow for 25,000 descriptors
this is a great number.
but in some scenarios it's overkill, and it's theoretically possible that
it might be underkill in others (citation needed), so add some handling
for both cases to save small amounts of vram on average and not crash
in the distant future when hypercomputers try running drawoverhead
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/21246>
Mike Blumenkrantz
4cda98c827