Back navigation using TopLevel.BackRequested does not work when a SplitView in Overlay mode is involved #21740

Describe the bug

When having a UI with a splitview and it is configured in overlay mode (e.g. mobile phone narrow screens), navigating back using the system back button (e.g. Android back button or navigate back gesture) does not work:
Nothing happens.

This is due to the fact that SplitView "steals" the event even if its Pane is not open!
PR will follow shortly!!

To Reproduce

Open a page containing a splitview configured in overlay mode on your mobile (e.g. android phone)
Try navigating back using the back gesture or back button - done

Expected behavior

Back navigation should work.
If the pane is open (in overlay mode) the pane should close
Otherwise the SplitView should ignore the event and not set "Handled=true"

Avalonia version

12.0.5 and 11.x

OS

No response

Additional context

No response