nir/algebraic: sqrt(x)*sqrt(x) -> fabs(x)

nir/algebraic: sqrt(x)*sqrt(x) -> fabs(x)

total instructions in shared programs: 12840840 -> 12839341 (-0.01%)
instructions in affected programs: 122581 -> 121082 (-1.22%)
helped: 559
HURT: 0

total cycles in shared programs: 302505756 -> 302490031 (<.01%)
cycles in affected programs: 2022900 -> 2007175 (-0.78%)
helped: 1090
HURT: 130

Signed-off-by: Elie Tournier <elie.tournier@collabora.com>
Reviewed-by: Matt Turner <mattst88@gmail.com>
Tested-by: Marge Bot <https://gitlab.freedesktop.org/mesa/mesa/merge_requests/948>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/merge_requests/948>