Ensure the vertical text alignment is updated when the Text height changes.

Task-number: QTBUG-31647

Change-Id: Ia0968a7a40c40411df5b3ed841a42f6cef141525
Reviewed-by: Andrew Knight <andrew.knight@digia.com>
Reviewed-by: Vesa Halttunen
Reviewed-by: Alan Alpert <aalpert@blackberry.com>