compositor: Store original output scale

We want this so we can restore the original mode
with the original size (after having been fullscreen).

src/compositor.c

@@ -2697,6 +2697,7 @@ weston_output_init(struct weston_output *output, struct weston_compositor *c,
 	output->mm_width = mm_width;
 	output->mm_height = mm_height;
 	output->dirty = 1;
+	output->origin_scale = scale;
 
 	weston_output_transform_scale_init(output, transform, scale);
 	weston_output_init_zoom(output);

src/compositor.h

@@ -187,6 +187,7 @@ struct weston_output {
 
 	struct weston_mode *current;
 	struct weston_mode *origin;
+	int32_t origin_scale;
 	struct wl_list mode_list;
 
 	void (*start_repaint_loop)(struct weston_output *output);