spirv: Handle OOB vector extract operations

spirv: Handle OOB vector extract operations

We use vtn_vector_extract to handle vector component level derefs.  This
makes us gracefully handle the case where your vector component is OOB
and give you an undef.  The SPIR-V working group is still working out
whether or not this is technically legal but it's very little code for
us to handle it so we may as well.

Cc: mesa-stable@lists.freedesktop.org
Reviewed-by: Caio Marcelo de Oliveira Filho <caio.oliveira@intel.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/4495>