nir: add assertions that loops don't have a Continue Construct

Hoping that I didn't miss any, this *should* add assertions
to all functions and passes which explicitly handle 'nir_loop'.

Acked-by: Faith Ekstrand <faith.ekstrand@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/13962>

src/compiler/nir/nir_sweep.c

@@ -109,6 +109,7 @@ sweep_if(nir_shader *nir, nir_if *iff)
 static void
 sweep_loop(nir_shader *nir, nir_loop *loop)
 {
+   assert(!nir_loop_has_continue_construct(loop));
    ralloc_steal(nir, loop);
 
    foreach_list_typed(nir_cf_node, cf_node, node, &loop->body) {