Fix alt down shortcuts and allow alt down handling for end users (#6491)

* [Menu] [Interaction] Allow end user to change menu show delay globally

* Fix all alt down handle = true by AccessKeyHandler

Co-authored-by: Max Katz <maxkatz6@outlook.com>

src/Avalonia.Input/AccessKeyHandler.cs

@@ -157,10 +157,9 @@ namespace Avalonia.Input
 
                     _restoreFocusElement?.Focus();
                     _restoreFocusElement = null;
+                    
+                    e.Handled = true;
                 }
-
-                // We always handle the Alt key.
-                e.Handled = true;
             }
             else if (_altIsDown)
             {