Add optimized "overloads" to QSGCurveProcessor

QSGCurveProcessor offers processFill(QQuadPath, ...) and processStroke(QQuadPath, ...) to add data to QSGCurveFillNode and QSGCurveStrokeNode.

It would be great to also add processFill(QPolygonF, ...) and processStroke(QPolylineF, ...).
These should be accompanied by the respective QSGLineFillNode or QSGLineStrokeNode (please find better names).

The idea is to have a highly optimized code path that allows for example fast vector map rendering but also improvments with vectorgraphics that have mostly lines.