nir/algebraic: optimize Cyberpunk 2077's open-coded bitfieldReverse()
fossil-db (Sienna Cichlid):
Totals from 9 (0.01% of 128647) affected shaders:
CodeSize: 29900 -> 28640 (-4.21%)
Instrs: 5677 -> 5443 (-4.12%)
Latency: 96561 -> 95025 (-1.59%)
Copies: 571 -> 544 (-4.73%)