Fix menu items being clickable during fade out

[peppy]

Addresses concerns cited in ppy/osu#32735.

[bdach]

While setting these will indeed prevent the other menu items from being clicked, it will also allow mouse input to fall through the context menu to whatever is behind it.

In the test you modified here, that can be exercised by

diff --git a/osu.Framework.Tests/Visual/UserInterface/TestSceneClosableMenu.cs b/osu.Framework.Tests/Visual/UserInterface/TestSceneClosableMenu.cs
index 9d7959e8b..33657ab3a 100644
--- a/osu.Framework.Tests/Visual/UserInterface/TestSceneClosableMenu.cs
+++ b/osu.Framework.Tests/Visual/UserInterface/TestSceneClosableMenu.cs
@@ -131,6 +131,7 @@ public void TestItemsNotClickableDuringFadeOut()
             bool item1Clicked = false;
             bool item2Clicked = false;
             bool topLevelItemClicked = false;
+            bool backgroundClickReceived = false;
 
             AddStep("set item actions", () =>
             {
@@ -138,15 +139,23 @@ public void TestItemsNotClickableDuringFadeOut()
                 Menus.GetSubMenu(0).Items[0].Items[1].Action.Value = () => item2Clicked = true;
                 Menus.GetSubMenu(0).Items[1].Action.Value = () => topLevelItemClicked = true;
             });
+            AddStep("add mouse handler", () => Add(new MouseHandlingLayer
+            {
+                Action = () => backgroundClickReceived = true,
+                Depth = 1,
+            }));
 
             AddStep("click item", () => ClickItem(0, 0));
             AddStep("click item", () => ClickItem(1, 0));
             AddAssert("menu item 1 activated", () => item1Clicked);
+
             AddStep("click item", () => ClickItem(1, 1));
             AddAssert("menu item 2 not activated", () => !item2Clicked);
+            AddAssert("background did not receive click", () => !backgroundClickReceived);
 
             AddStep("click top level item", () => ClickItem(0, 1));
             AddAssert("top level item not activated", () => !topLevelItemClicked);
+            AddAssert("background did not receive click", () => !backgroundClickReceived);
         }
 
         private partial class MouseHandlingLayer : Drawable

Do you see this as a problem?

[peppy]

I don't. At the point the menu is "closed", we can assume it's transitioning away from existence. From a user's perspective, they should be able to interact behind it (else they will have to learn that their clicks may be blocked for n milliseconds after dismissing a menu).

So I'd argue what is in this PR is more correct than trying to block during that duration.

[bdach]

I guess we shall see what "hilarious" input handling issues, if any, shall come of this

[peppy]

FWIW i already ran all osu tests against this change.