nir/opt_algebraic: Simple xor/ishr optimizations.

nir/opt_algebraic: Simple xor/ishr optimizations.

The first pattern here removes the xor-swap pattern.

Foz-DB GFX10_3:
Totals from 305 (0.23% of 134913) affected shaders:
CodeSize: 1589040 -> 1585164 (-0.24%)
Instrs: 284344 -> 283375 (-0.34%)
Latency: 4205148 -> 4198472 (-0.16%); split: -0.16%, +0.00%
InvThroughput: 708745 -> 708739 (-0.00%)

Signed-off-by: Georg Lehmann <dadschoorse@gmail.com>
Reviewed-by: Alyssa Rosenzweig <alyssa@collabora.com>
Reviewed-by: Timur Kristóf <timur.kristof@gmail.com>
Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/16411>