nir/opt_vectorize: hash whether a swizzle accesses elements beyond the maximum vector...

nir/opt_vectorize: hash whether a swizzle accesses elements beyond the maximum vectorization factor

Swizzles that access components outside of the maximum
vector size cannot be vectorized with each other.
This patch creates different hash bins for this case.

For example accesses to .x and .y are considered different variables
compared to accesses to .z and .w for 16-bit vec2.

This prevents the vectorization of things like
   vec2 16 ssa_3 = iadd ssa_1.xz, ssa_2.xz

Reviewed-by: Connor Abbott <cwabbott0@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/6666>