fdo#54320: VoiceOver does not follow keyboard focus

The AXFocusedUIElementChanged notification must have the application object
as its parameter, as it is the application object whose AXFocusedUIElement
attribute value is changing (and because the docs say so).

Change-Id: Ife63a1e59d8a24256ace38fb98b69fd1544f9c96
Reviewed-on: https://gerrit.libreoffice.org/5155Reviewed-by: Norbert Thiebaud <nthiebaud@gmail.com>
Tested-by: Norbert Thiebaud <nthiebaud@gmail.com>

vcl/aqua/source/a11y/aqua11yfocuslistener.cxx

@@ -83,7 +83,7 @@ AquaA11yFocusListener::focusedObjectChanged(const Reference< XAccessible >& xAcc
             if( xContext.is() )
             {
                 m_focusedObject = [ AquaA11yFactory wrapperForAccessibleContext: xContext ];
-                NSAccessibilityPostNotification(m_focusedObject, NSAccessibilityFocusedUIElementChangedNotification);
+                NSAccessibilityPostNotification(NSApp, NSAccessibilityFocusedUIElementChangedNotification);
             }
         }
     } catch(const RuntimeException &) {