intel/fs: Allow cmod propagation to instructions with saturate modifier

intel/fs: Allow cmod propagation to instructions with saturate modifier

v2: Add unit tests.  Suggested by Matt.

All Intel GPUs had similar results. (Ice Lake shown)
total instructions in shared programs: 17229441 -> 17228658 (<.01%)
instructions in affected programs: 159574 -> 158791 (-0.49%)
helped: 489
HURT: 0
helped stats (abs) min: 1 max: 5 x̄: 1.60 x̃: 1
helped stats (rel) min: 0.07% max: 2.70% x̄: 0.61% x̃: 0.59%
95% mean confidence interval for instructions value: -1.72 -1.48
95% mean confidence interval for instructions %-change: -0.64% -0.58%
Instructions are helped.

total cycles in shared programs: 360944149 -> 360937144 (<.01%)
cycles in affected programs: 1072195 -> 1065190 (-0.65%)
helped: 254
HURT: 27
helped stats (abs) min: 2 max: 234 x̄: 30.51 x̃: 9
helped stats (rel) min: 0.04% max: 8.99% x̄: 0.75% x̃: 0.24%
HURT stats (abs)   min: 2 max: 83 x̄: 27.56 x̃: 24
HURT stats (rel)   min: 0.09% max: 3.79% x̄: 1.28% x̃: 1.16%
95% mean confidence interval for cycles value: -30.11 -19.75
95% mean confidence interval for cycles %-change: -0.70% -0.41%
Cycles are helped.

Reviewed-by: Matt Turner <mattst88@gmail.com> [v1]