Use pixman_transform_point_31_16() from pixman_transform_point()

Use pixman_transform_point_31_16() from pixman_transform_point()

Old functions pixman_transform_point() and pixman_transform_point_3d()
now become just wrappers for pixman_transform_point_31_16() and
pixman_transform_point_31_16_3d(). Eventually their uses should be
completely eliminated in the pixman code and replaced with their
extended range counterparts. This is needed in order to be able
to correctly handle any matrices and parameters that may come
to pixman from the code responsible for XRender implementation.