Adjust drag to pull down notifications to avoid desktop mode app handle

When desktop mode is enabled an app handle now appears in the centre of
the status bar which allows entry to desktop mode via a drag down. As a
result the notifications shade can now longer be accesed via this
central region in the status bar. So we have shifted the drag to pull
the notification in this test to avoid the app handle.

Bug: 331917542
Test: atest EnterSplitScreenByDragFromNotificationGesturalNavPortrait
atest EnterSplitScreenByDragFromNotificationGesturalNavLandscape

Change-Id: Id3704886d93812176ef7acb6b9c27e8b4ec06df7