FillGradientPrimitive2D/ and PolyPolygonGradientPrimitive2D now support both alphas, a gradientAlpha and a unified one. This allows a processor to directly handle a gradient with a unifiedAlpha if he wants. Adapted other places accordingly. NOTE: In VclMetafileProcessor2D handling of the primitive PolyPolygonGradientPrimitive2D has to do a local compromize, see comment there. Change-Id: I536f4935dafde0369f768dbd281d547b7bb08eb4 Reviewed-on: https://gerrit.libreoffice.org/c/core/+/171052 Reviewed-by: Armin Le Grand <Armin.Le.Grand@me.com> Tested-by: Jenkins