view: Save surface x and y on saved buffers

We need to use surface_x and surface_y when rendering and damaging saved
buffers as these compensate for views that have been centered due to
being smaller than their container.

Add them to the surface positions on the saved buffer so we have the
values from the time the buffer was saved.

sway/desktop/render.c

@@ -289,10 +289,8 @@ static void render_saved_view(struct sway_view *view,
 		}
 
 		struct wlr_box box = {
-			.x = view->container->surface_x - output->lx -
+			.x = saved_buf->x - view->saved_geometry.x - output->lx,
-				view->saved_geometry.x + saved_buf->x,
+			.y = saved_buf->y - view->saved_geometry.y - output->ly,
-			.y = view->container->surface_y - output->ly -
-				view->saved_geometry.y + saved_buf->y,
 			.width = saved_buf->width,
 			.height = saved_buf->height,
 		};

sway/desktop/transaction.c

@@ -214,8 +214,8 @@ static void apply_container_state(struct sway_container *container,
 		struct sway_saved_buffer *saved_buf;
 		wl_list_for_each(saved_buf, &view->saved_buffers, link) {
 			struct wlr_box box = {
-				.x = container->current.content_x - view->saved_geometry.x + saved_buf->x,
+				.x = saved_buf->x - view->saved_geometry.x,
-				.y = container->current.content_y - view->saved_geometry.y + saved_buf->y,
+				.y = saved_buf->y - view->saved_geometry.y,
 				.width = saved_buf->width,
 				.height = saved_buf->height,
 			};

sway/tree/view.c

@@ -1350,8 +1350,8 @@ static void view_save_buffer_iterator(struct wlr_surface *surface,
 		saved_buffer->buffer = surface->buffer;
 		saved_buffer->width = surface->current.width;
 		saved_buffer->height = surface->current.height;
-		saved_buffer->x = sx;
+		saved_buffer->x = view->container->surface_x + sx;
-		saved_buffer->y = sy;
+		saved_buffer->y = view->container->surface_y + sy;
 		saved_buffer->transform = surface->current.transform;
 		wlr_surface_get_buffer_source_box(surface, &saved_buffer->source_box);
 		wl_list_insert(&view->saved_buffers, &saved_buffer->link);