shell: Respect output transformation for input panel surface

Rather than using the dimensions in the mode we can use the recently
added output width and height members which are updated to reflect any
output rotation.

https://bugs.freedesktop.org/show_bug.cgi?id=66798

src/shell.c

@@ -3732,7 +3732,6 @@ input_panel_configure(struct weston_surface *surface, int32_t sx, int32_t sy, in
 {
 	struct input_panel_surface *ip_surface = surface->configure_private;
 	struct desktop_shell *shell = ip_surface->shell;
-	struct weston_mode *mode;
 	float x, y;
 	uint32_t show_surface = 0;
 
@@ -3752,10 +3751,8 @@ input_panel_configure(struct weston_surface *surface, int32_t sx, int32_t sy, in
 		x = shell->text_input.surface->geometry.x + shell->text_input.cursor_rectangle.x2;
 		y = shell->text_input.surface->geometry.y + shell->text_input.cursor_rectangle.y2;
 	} else {
-		mode = ip_surface->output->current;
+		x = ip_surface->output->x + (ip_surface->output->width - width) / 2;
-
+		y = ip_surface->output->y + ip_surface->output->height - height;
-		x = ip_surface->output->x + (mode->width - width) / 2;
-		y = ip_surface->output->y + mode->height - height;
 	}
 
 	weston_surface_configure(surface,