Define the {de,}initialization functions in the bindings

The extension creators then don't need to create those just to redirect
to the bindings.

src/godot.cpp

@@ -80,3 +80,14 @@ void GDExtensionBinding::free_instance_callback(void *p_token, void *p_instance,
 }
 
 } // namespace godot
+
+extern "C" {
+
+void GDN_EXPORT initialize_level(void *userdata, GDNativeInitializationLevel p_level) {
+	godot::GDExtensionBinding::initialize_level(userdata, p_level);
+}
+
+void GDN_EXPORT deinitialize_level(void *userdata, GDNativeInitializationLevel p_level) {
+	godot::GDExtensionBinding::deinitialize_level(userdata, p_level);
+}
+}

test/src/register_types.cpp

@@ -29,12 +29,4 @@ GDNativeBool GDN_EXPORT example_library_init(const GDNativeInterface *p_interfac
 
 	return result;
 }
-
-void GDN_EXPORT initialize_level(void *userdata, GDNativeInitializationLevel p_level) {
-	godot::GDExtensionBinding::initialize_level(userdata, p_level);
-}
-
-void GDN_EXPORT deinitialize_level(void *userdata, GDNativeInitializationLevel p_level) {
-	godot::GDExtensionBinding::deinitialize_level(userdata, p_level);
-}
 }