Schedule adding transforms on tablet changes

Fixes `InvalidThreadForMutationException`s that pop up when
disconnecting/reconnecting tablets during the game's operation. In those
cases the value change callback executes from  an OpenTabletDriver
thread.

osu.Game/Overlays/Settings/Sections/Input/TabletAreaSelection.cs

@@ -125,17 +125,20 @@ namespace osu.Game.Overlays.Settings.Sections.Input
             }, true);
 
             tablet.BindTo(handler.Tablet);
-            tablet.BindValueChanged(val =>
+            tablet.BindValueChanged(_ => Scheduler.AddOnce(updateTabletDetails));
-            {
-                tabletContainer.Size = val.NewValue?.Size ?? Vector2.Zero;
-                tabletName.Text = val.NewValue?.Name ?? string.Empty;
-                checkBounds();
-            }, true);
 
+            updateTabletDetails();
             // initial animation should be instant.
             FinishTransforms(true);
         }
 
+        private void updateTabletDetails()
+        {
+            tabletContainer.Size = tablet.Value?.Size ?? Vector2.Zero;
+            tabletName.Text = tablet.Value?.Name ?? string.Empty;
+            checkBounds();
+        }
+
         private static int greatestCommonDivider(int a, int b)
         {
             while (b != 0)

osu.Game/Overlays/Settings/Sections/Input/TabletSettings.cs

@@ -196,19 +196,13 @@ namespace osu.Game.Overlays.Settings.Sections.Input
             tablet.BindTo(tabletHandler.Tablet);
             tablet.BindValueChanged(val =>
             {
+                Scheduler.AddOnce(toggleVisibility);
+
                 var tab = val.NewValue;
 
                 bool tabletFound = tab != null;
-
                 if (!tabletFound)
-                {
-                    mainSettings.Hide();
-                    noTabletMessage.Show();
                     return;
-                }
-
-                mainSettings.Show();
-                noTabletMessage.Hide();
 
                 offsetX.MaxValue = tab.Size.X;
                 offsetX.Default = tab.Size.X / 2;
@@ -222,6 +216,21 @@ namespace osu.Game.Overlays.Settings.Sections.Input
             }, true);
         }
 
+        private void toggleVisibility()
+        {
+            bool tabletFound = tablet.Value != null;
+
+            if (!tabletFound)
+            {
+                mainSettings.Hide();
+                noTabletMessage.Show();
+                return;
+            }
+
+            mainSettings.Show();
+            noTabletMessage.Hide();
+        }
+
         private void applyAspectRatio(BindableNumber<float> sizeChanged)
         {
             try