Fix dropdown margins and animations being weird

This was attempted to be fixed by frenzibyte using some hack workaround
logic, but this is the true fix.

Things were never matching due to `UpdateSize` spamming `Resize`
transforms every frame, causing the fade out to complete before
transforms have reached a final state.

osu.Game/Graphics/UserInterface/OsuDropdown.cs

@@ -104,9 +104,17 @@ namespace osu.Game.Graphics.UserInterface
                 }
             }
 
+            private Vector2? targetSize;
+
             // todo: this uses the same styling as OsuMenu. hopefully we can just use OsuMenu in the future with some refactoring
             protected override void UpdateSize(Vector2 newSize)
             {
+                // TODO: should probably fix this at a framework level (this method is running every frame which can spam transforms)
+                if (newSize == targetSize)
+                    return;
+
+                targetSize = newSize;
+
                 if (Direction == Direction.Vertical)
                 {
                     Width = newSize.X;