Gets the output intent in effect for the content being run: the page's first output intent with a profile, else the
document's, or null. Not a graphics state parameter; carried here so every conversion made from the state
can honour it.
public PdfOutputIntent? OutputIntent { get; }
ISO 32000-2 §14.11.5 (a page-level output intent is used for its page). Set by the interpreter when a run starts and kept by
nested runs; gs does not change it. FromState(in GraphicsState, DeviceColorModel) passes it on.