Adds a patch whose corners carry colours.
public PdfPatchMeshBuilder AddPatch(ReadOnlySpan<PathPoint> controlPoints, ReadOnlySpan<PdfColor> cornerColors)
The control points, in data-stream order: 12 for a Coons patch, 16 for a tensor-product patch.
The colours at p00, p03, p33 and p30.
ISO 32000-2 Table 84 (f = 0).