Rename frame_create and frame_set_child_size with a window_ prefix

This is to avoid a collision with an actual frame structure.

Signed-off-by: Jason Ekstrand <jason@jlekstrand.net>
diff --git a/clients/subsurfaces.c b/clients/subsurfaces.c
index 101ff17..0f11009 100644
--- a/clients/subsurfaces.c
+++ b/clients/subsurfaces.c
@@ -722,7 +722,7 @@
 	display_set_user_data(app->display, app);
 
 	app->window = window_create(app->display);
-	app->widget = frame_create(app->window, app);
+	app->widget = window_frame_create(app->window, app);
 	window_set_title(app->window, "Wayland Sub-surface Demo");
 
 	window_set_key_handler(app->window, key_handler);