nir/opt_uniform_atomics: recognize more complicated invocation comparisons

nir/opt_uniform_atomics: recognize more complicated invocation comparisons

For example, gl_LocalInvocationID.x + gl_LocalInvocationID.y * 8.

fossil-db (GFX10.3):
Totals from 8 (0.01% of 139391) affected shaders:
CodeSize: 15224 -> 14800 (-2.79%)
Instrs: 2880 -> 2798 (-2.85%)
Cycles: 44556 -> 44204 (-0.79%)
VMEM: 407 -> 473 (+16.22%); split: +17.69%, -1.47%
Copies: 491 -> 483 (-1.63%)
Branches: 200 -> 192 (-4.00%)

Signed-off-by: Rhys Perry <pendingchaos02@gmail.com>
Reviewed-by: Daniel Schürmann <daniel@schuermann.dev>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/8654>