Fix gradient fill under group shape transform

When a gradient fill is defined in an outer group and a shape sits inside
an inner group with its own ShapeTransform, QPainter's world transform
was applied to both the path and the gradient coordinates, causing the
gradient to be incorrectly shifted and rotated.

Pick-to: 6.12
Task-number: QTBUG-147789
Change-Id: I1e6c16e407175c111d9ee6b38146cc5b87072190
Reviewed-by: Eskil Abrahamsen Blomfeldt <eskil.abrahamsen-blomfeldt@qt.io>