Support per-plane strides and data offsets in QVideoFrame.

Since just adding a new virtual isn't binary compatible add a new derivative
type with a virtual member and connect it up through a virtual in the private
class.

[ChangeLog] Support for per-plane strides and data offsets in QVideoFrame.

Task-number: QTBUG-38345
Change-Id: I1974c2b0b454d130e17971ce549031259d61f9cd
Reviewed-by: Yoann Lopes <yoann.lopes@digia.com>