Make module information lookup from runtime safe.

This commit uses a two-phase lookup of stack map information from modules
rather than giving back raw pointers to stack maps.

First the runtime looks up information about a module from a pc value, which
returns an `Arc` it keeps a reference on while completing the stack map lookup.

Second it then queries the module information for the stack map from a pc
value, getting a reference to the stack map (which is now safe because of the
`Arc` held by the runtime).

crates/runtime/src/instance/allocator/pooling/uffd.rs

@@ -523,7 +523,7 @@ mod test {
                                 host_state: Box::new(()),
                                 interrupts: ptr::null(),
                                 externref_activations_table: ptr::null_mut(),
-                                stack_map_lookup: None,
+                                module_info_lookup: None,
                             },
                         )
                         .expect("instance should allocate"),