It came up during 6.2 API review that we prefer all floating-point API
to be double-precision on 64-bit platforms, despite the awkwardness of
representing a displacement vector with something called a "point".
The docs for QPointF explicitly state "A QPointF object can also be used
as a vector: Addition and subtraction are defined..."
Amends 31f90e99b8
Change-Id: I01029661f2586640cbf846f49df164c176d17f7a
Reviewed-by: Volker Hilsheimer <volker.hilsheimer@qt.io>
e3aa45006d