nir: add a nir_get_ubo_size intrinsic

This is the same as nir_get_buffer_size but geared towards UBOs instead
of SSBOs. The new intrinsic is useful in Vulkan backends that need to
add bound checks on buffer accesses to honor the robust buffer access
feature.

Reviewed-by: Alejandro Piñeiro <apinheiro@igalia.com>
Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/6766>

src/compiler/nir/nir_intrinsics.py

@@ -209,6 +209,8 @@ intrinsic("deref_buffer_array_length", src_comp=[-1], dest_comp=1,
 # as source.
 intrinsic("get_ssbo_size", src_comp=[-1], dest_comp=1,
           flags=[CAN_ELIMINATE, CAN_REORDER])
+intrinsic("get_ubo_size", src_comp=[-1], dest_comp=1,
+          flags=[CAN_ELIMINATE, CAN_REORDER])
 
 # a barrier is an intrinsic with no inputs/outputs but which can't be moved
 # around/optimized in general