CL: Mangle libclc names using vtn_type instead of glsl_type

This patch lets us get away with adding the OpenCL event_t type only to vtn, without adding it to nir. It also means we don't have to pass address space data in parallel to the types, since vtn encodes that directly in the vtn_type struct for pointers.

This will be incorporated into mesa/mesa!6035 (merged) for upstream submission, to replace mesa/mesa@ed1afa62, and means that we don't need mesa/mesa!6038 (closed).

/cc @jekstrand