aco/insert_exec_mask: stay in WQM while helper lanes are still needed

aco/insert_exec_mask: stay in WQM while helper lanes are still needed

This patch flags all instructions WQM which don't require
Exact mode, but depend on the exec mask as long as WQM
is needed on any control flow path afterwards.
This will mostly prevent accidental copies of WQM values
within Exact mode, and also makes a lot of other workarounds
unnecessary.

Totals from 17374 (12.88% of 134913) affected shaders: (GFX10.3)
VGPRs: 526952 -> 527384 (+0.08%); split: -0.01%, +0.09%
CodeSize: 33740512 -> 33766636 (+0.08%); split: -0.06%, +0.14%
MaxWaves: 488166 -> 488108 (-0.01%); split: +0.00%, -0.02%
Instrs: 6254240 -> 6260557 (+0.10%); split: -0.08%, +0.18%
Latency: 66497580 -> 66463472 (-0.05%); split: -0.15%, +0.10%
InvThroughput: 13265741 -> 13264036 (-0.01%); split: -0.03%, +0.01%
VClause: 122962 -> 122975 (+0.01%); split: -0.01%, +0.02%
SClause: 334805 -> 334405 (-0.12%); split: -0.51%, +0.39%
Copies: 275728 -> 282341 (+2.40%); split: -0.91%, +3.31%
Branches: 92546 -> 90990 (-1.68%); split: -1.68%, +0.00%
PreSGPRs: 504119 -> 504352 (+0.05%); split: -0.00%, +0.05%

Reviewed-by: Rhys Perry <pendingchaos02@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/14951>