PDFViewer control for Desktop Apps

Web projects gained a PDFViewer control in the current release: load a PDF from bytes or a project resource, page through it, zoom, and react to load, page and zoom changes. Desktop apps have no equivalent today; showing a PDF means shelling out to an external viewer or embedding an entire browser through HTMLViewer.

Requested change: add a PDFViewer control to the desktop control library with matching functionality.

• Load a document from a MemoryBlock (optionally naming it) or from a project resource with LoadResource, and clear the viewer with Clear.
• Read document state: PageCount, PageIndex (also settable for page navigation), DocumentName, IsLoaded, IsLoading, EffectiveZoom, ErrorCode and ErrorMessage.
• Control the view: Zoom (0.1 to 8.0), ZoomMode (PDFZoomMode.Custom, FitWidth or FitPage) and ShowToolbar.
• React to the document and view: DocumentLoaded, LoadFailed, PageChanged and ZoomChanged events.
• The PDFZoomMode and PDFViewerError enums use the same names and values as the Web control, so shared code written against the Web PDFViewer compiles unchanged for desktop.