agx: Add CSE optimization pass

agx: Add CSE optimization pass

Ported from the Bifrost compiler, in turn based on the ir3 one. This
cleans up a lot of junk we emit during NIR->AGX and will help with some
SSA RA troubles.

total instructions in shared programs: 34803 -> 34381 (-1.21%)
instructions in affected programs: 18652 -> 18230 (-2.26%)
helped: 198
HURT: 0
helped stats (abs) min: 1.0 max: 28.0 x̄: 2.13 x̃: 1
helped stats (rel) min: 0.31% max: 12.50% x̄: 3.94% x̃: 2.78%
95% mean confidence interval for instructions value: -2.45 -1.81
95% mean confidence interval for instructions %-change: -4.40% -3.48%
Instructions are helped.

total bytes in shared programs: 238094 -> 234824 (-1.37%)
bytes in affected programs: 126472 -> 123202 (-2.59%)
helped: 200
HURT: 0
helped stats (abs) min: 6.0 max: 168.0 x̄: 16.35 x̃: 8
helped stats (rel) min: 0.37% max: 17.65% x̄: 4.25% x̃: 3.38%
95% mean confidence interval for bytes value: -18.49 -14.21
95% mean confidence interval for bytes %-change: -4.67% -3.84%
Bytes are helped.

total halfregs in shared programs: 10078 -> 10107 (0.29%)
halfregs in affected programs: 565 -> 594 (5.13%)
helped: 22
HURT: 22
helped stats (abs) min: 1.0 max: 4.0 x̄: 1.23 x̃: 1
helped stats (rel) min: 5.71% max: 25.00% x̄: 23.38% x̃: 25.00%
HURT stats (abs)   min: 2.0 max: 4.0 x̄: 2.55 x̃: 2
HURT stats (rel)   min: 4.44% max: 30.77% x̄: 15.61% x̃: 12.73%
95% mean confidence interval for halfregs value: 0.03 1.28
95% mean confidence interval for halfregs %-change: -10.17% 2.40%
Inconclusive result (%-change mean confidence interval includes 0).

Signed-off-by: Alyssa Rosenzweig <alyssa@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/19590>