doc: Clarify focus window vs activation in Key Handling Overview

Pick-to: 6.6 6.5 6.2
Change-Id: I837e72448577e6814acf20cef49f4528e2ac6ba7
Reviewed-by: Axel Spoerl <axel.spoerl@qt.io>

Author: torarnv

src/quick/doc/src/concepts/input/focus.qdoc

@@ -18,8 +18,8 @@ scope based extension to Qt's traditional keyboard focus model.
 When the user presses or releases a key, the following occurs:
 \list 1
 \li Qt receives the key action and generates a key event.
-\li If a \l QQuickWindow is the active window, the key event
-is delivered to it.
+\li If a \l QQuickWindow is the \l{QGuiApplication::focusWindow()}{focus window}
+of the application, the key event is delivered to it.
 \li The key event is delivered by the scene to the \l Item with
 \e {active focus}. If no item has active focus, the key event is ignored.
 \li If the \l QQuickItem with active focus accepts the key event, propagation