Fix sheared button getting cut when scaled beyond 100%

Keep masking back in `Content`, since the scaling animation is happening
on `Content` instead of `this`. This doesn't regress the intended
behaviour in this PR (which is to just to make the button class itself
sheared instead of its content).

osu.Game/Graphics/UserInterface/ShearedButton.cs

@@ -89,11 +89,11 @@ namespace osu.Game.Graphics.UserInterface
         {
             Height = height;
 
-            CornerRadius = CORNER_RADIUS;
             Shear = OsuGame.SHEAR;
-            Masking = true;
 
             Content.Anchor = Content.Origin = Anchor.Centre;
+            Content.CornerRadius = CORNER_RADIUS;
+            Content.Masking = true;
 
             Children = new Drawable[]
             {