Initializes a new instance of the ProgressiveZoom class and shows viewport.
public ProgressiveZoom(TileScheduler scheduler, in Viewport viewport, ProgressiveZoomOptions? options = null)
The scheduler that renders the tiles; the zoom drives its Update(in Viewport).
The viewport to start from (its zoom is kept as given).
The zoom range and settle delay, or null for defaults.
Spec #33 viewer capability 2.