Support binding y-inverted pixmaps as QBrushes

Most texture-from-pixmap implementations don't support inverting the y coordinate for bound pixmaps, making them bind up-side-down. The GL2 paint engine supports flipping the pixmaps back the correct way up by inverting the texture coordinates. However, this only works for drawPixmap. It would be great if we could support inverting the coordinates for a QBrush's pixmap too. This would make it possible to use texture-from-pixmap for QBrushs. Also, the GL2 doesn't currently implement drawTiledPixmap, falling back to the base implementation which uses fillRect with a pixmap brush. So implementing this would also allow drawTiledPixmap to use texture-from-pixmap too.