aco/optimizer: check recursively if we can eliminate s_and exec

aco/optimizer: check recursively if we can eliminate s_and exec

Totals from 2860 (2.12% of 134913) affected shaders: (GFX10.3)
CodeSize: 5990728 -> 5979164 (-0.19%); split: -0.20%, +0.01%
Instrs: 1094562 -> 1091653 (-0.27%); split: -0.28%, +0.01%
Latency: 8689841 -> 8684523 (-0.06%); split: -0.07%, +0.00%
InvThroughput: 1840533 -> 1840527 (-0.00%); split: -0.00%, +0.00%
SClause: 51437 -> 51439 (+0.00%)
Copies: 82461 -> 82472 (+0.01%)
PreSGPRs: 83136 -> 83172 (+0.04%)

Reviewed-by: Timur Kristóf <timur.kristof@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/15675>