Fix Text baselineOffset caclulations.

Update the baselineOffset when short cutting layout due to an empty
text property.  And allow alterations to the baseline due to images,
font scaling and custom layouts when doing a layout.

Task-number: QTBUG-24303
Change-Id: I5a31a6108cded490fef8b0674e15558ea4e22d6b
Reviewed-by: Michael Brasser <michael.brasser@nokia.com>