* Changes necessary for making SharpTreeNode cross platform by proxying System.Windows dependencies
* Add ITreeNodeImagesProvider for node icons
* Move InternalsVisibleTo to csproj (possible since net50)
* Move view models and other xplat class for SharpTreeView to ILSpyX, Windows-dependent classes to ILSpy/Controls/TreeView
* Move GetDoubleClickTime to NativeMethods