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.rs

@@ -1370,7 +1370,7 @@ mod test {
                             host_state: Box::new(()),
                             interrupts: std::ptr::null(),
                             externref_activations_table: std::ptr::null_mut(),
-                            stack_map_lookup: None,
+                            module_info_lookup: None,
                         },
                     )
                     .expect("allocation should succeed"),
@@ -1394,7 +1394,7 @@ mod test {
                 host_state: Box::new(()),
                 interrupts: std::ptr::null(),
                 externref_activations_table: std::ptr::null_mut(),
-                stack_map_lookup: None,
+                module_info_lookup: None,
             },
         ) {
             Err(InstantiationError::Limit(3)) => {}