r300: Request NIR shaders from mesa/st and use NIR-to-TGSI.

r300: Request NIR shaders from mesa/st and use NIR-to-TGSI.

This brings us into parity on state tracker paths with most other
supported drivers, and a lot of additional optimization on our shaders.

Results on a subset of shader-db that doesn't crash:

instructions in affected programs: 59502 -> 47991 (-19.35%)
vinst in affected programs: 17633 -> 15197 (-13.82%)
sinst in affected programs: 9296 -> 7319 (-21.27%)
flowcontrol in affected programs: 627 -> 310 (-50.56%)
presub in affected programs: 4220 -> 1554 (-63.18%)
temps in affected programs: 5775 -> 8570 (48.40%)
lits in affected programs: 215 -> 37 (-82.79%)

The temps (register usage) increase is unfortunate, but it seems that
instruction counts tend to be our limit before reg counts are.

Fixes: #3354
Reviewed-by: Marek Olšák <marek.olsak@amd.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/14096>