Force beatmap listing overlay's textbox back on screen when a key is pressed

Not the cleanest solution, but works for now. Will eventually be
replaced after the header is updated to reflect the latest designs
(which keeps it on screen in all cases).

Closes https://github.com/ppy/osu/issues/10703.

osu.Game/Overlays/BeatmapListingOverlay.cs

@@ -68,6 +68,7 @@ namespace osu.Game.Overlays
                             Header,
                             filterControl = new BeatmapListingFilterControl
                             {
+                                TypingStarted = onTypingStarted,
                                 SearchStarted = onSearchStarted,
                                 SearchFinished = onSearchFinished,
                             },
@@ -102,6 +103,12 @@ namespace osu.Game.Overlays
             };
         }
 
+        private void onTypingStarted()
+        {
+            // temporary until the textbox/header is updated to always stay on screen.
+            resultScrollContainer.ScrollToStart();
+        }
+
         protected override void OnFocus(FocusEvent e)
         {
             base.OnFocus(e);