broadcom/compiler: rewrite partial update liveness tracking

broadcom/compiler: rewrite partial update liveness tracking

The code we had for this was a work in progress and not finished. Also,
it was geared towards partial writes caused by output packing (i.e.
fp16) and was ignoring partial updates caused by conditional writes,
which are far more common in our case.

This change provides an implementation for tracking conditional writes
that works in tandem with the previous spill change to narrow liveness
for their spills.

Fixes register allocation failures in:
dEQP-VK.graphicsfuzz.spv-stable-maze-flatten-copy-composite

We also gain one shader from shader-db:

total instructions in shared programs: 13339969 -> 13338584 (-0.01%)
instructions in affected programs: 185520 -> 184135 (-0.75%)
helped: 375
HURT: 130
Instructions are helped.

total threads in shared programs: 412038 -> 412040 (<.01%)
threads in affected programs: 2 -> 4 (100.00%)
helped: 1
HURT: 0

total uniforms in shared programs: 3746581 -> 3746585 (<.01%)
uniforms in affected programs: 49 -> 53 (8.16%)
helped: 0
HURT: 1

total max-temps in shared programs: 2359960 -> 2359947 (<.01%)
max-temps in affected programs: 289 -> 276 (-4.50%)
helped: 7
HURT: 0
Max-temps are helped.

total sfu-stalls in shared programs: 34351 -> 34359 (0.02%)
sfu-stalls in affected programs: 218 -> 226 (3.67%)
helped: 35
HURT: 37
Inconclusive result (value mean confidence interval includes 0).

total inst-and-stalls in shared programs: 13374320 -> 13372943 (-0.01%)
inst-and-stalls in affected programs: 186653 -> 185276 (-0.74%)
helped: 373
HURT: 132
Inst-and-stalls are helped.

LOST:   0
GAINED: 1

Reviewed-by: Alejandro Piñeiro <apinheiro@igalia.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/12278>