Works out the viewport that shows a destination: its page scrolled to, then its left and top edge (XYZ, FitH,
FitV, FitR and the bounding-box forms) at the viewport's top-left corner when it has them. The zoom is kept.
public static Viewport GetDestinationViewport(PdfExplicitDestination destination, PageLayout layout, in Viewport viewport)
The destination, from Destination.
The layout.
The current viewport.
viewport when the destination has no page here.ISO 32000-2 §12.3.2.2, Table 149.