wayland: Scale accelerated relative pointer coordinates with emulated resolutions

The accelerated relative coordinates are always relative to the desktop resolution, and need to be scaled with emulated fullscreen resolutions for mouse movement to remain stable. Otherwise, pointer speeds will be too fast on emulated resolutions below the desktop resolution, and too slow on those above.

(cherry picked from commit 027df89ed367cf2a4f4b390bc933b3bd8e8471d5)

src/video/wayland/SDL_waylandevents.c

@@ -1023,8 +1023,8 @@ static void relative_pointer_handle_relative_motion(void *data,
             dx = wl_fixed_to_double(dx_unaccel_w);
             dy = wl_fixed_to_double(dy_unaccel_w);
         } else {
-            dx = wl_fixed_to_double(dx_w);
-            dy = wl_fixed_to_double(dy_w);
+            dx = wl_fixed_to_double(dx_w) * window->pointer_scale.x;
+            dy = wl_fixed_to_double(dy_w) * window->pointer_scale.y;
         }
 
         SDL_SendMouseMotion(timestamp, window->sdlwindow, input->pointer_id, true, (float)dx, (float)dy);