Support for .NET Single file publishing.

[ElektroKill]

.NET supports publishing an application into a single native executable file. This executable contains the actual .net assembly, runtime configuration files, symbols, etc. Currently dnSpyEx shows these assemblies as regular native assemblies. dnSpyEx should be able to unpack these types of files and display their contents in the treeview. An option to extract these files into a directory specified by the user could also be implemented.

[ElektroKill]

This feature will not make it into dnSpyEx 6.2 and has been put on hold. For more info check the comment on PR #49.