spirv: run nir_copy_prop before nir_rematerialize_derefs_in_use_blocks_impl

spirv: run nir_copy_prop before nir_rematerialize_derefs_in_use_blocks_impl

spirv_to_nir sometimes wraps derefs in vec2 or mov instructions as part of
its texture handling. These get in the way of
nir_rematerialize_derefs_in_use_blocks_impl. Running copy propagation
should get rid of the extra move instructions and get us back to intact
deref chains for everything except variable pointer use-cases.

fossil-db (Sienna Cichlid):
Totals from 6 (0.00% of 134572) affected shaders:
CodeSize: 92656 -> 93088 (+0.47%)
Instrs: 17060 -> 17138 (+0.46%)
Latency: 224408 -> 227539 (+1.40%)
InvThroughput: 37402 -> 37924 (+1.40%)
VClause: 408 -> 402 (-1.47%)
Copies: 1065 -> 1107 (+3.94%)

Signed-off-by: Rhys Perry <pendingchaos02@gmail.com>
Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>
Closes: https://gitlab.freedesktop.org/mesa/mesa/-/issues/5668
Fixes: 14a12b771d0 ("spirv: Rework our handling of images and samplers")
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/13924>