The slnf name was a leftover from when ILSpy.csproj was WPF; its
contents are now the Avalonia desktop projects. Drop the dead
ILSpy.BamlDecompiler.csproj ref (the directory no longer holds a
project after the engine moved to ICSharpCode.BamlDecompiler) and the
out-of-scope items (TestPlugin, ILSpy.BamlDecompiler.Tests) -- they're
in neither ILSpy.sln nor any active build flow, so the slnf filter
surfacing them in IDE listings was just noise.
Assisted-by: Claude:claude-opus-4-7:Claude Code
* 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