spirv: Add better checks for SSA value types

spirv: Add better checks for SSA value types

Primarily, we check for two things:

 1. That we only ever add SSA values via vtn_push_ssa_value and
    vtn_copy_value.

 2. That the type of the SSA value matches the SPIR-V destination type.

Reviewed-by: Caio Marcelo de Oliveira Filho <caio.oliveira@intel.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/5278>