.NET port

[Tichau]

Is your feature request related to a problem? Please describe.
In order to be able to migrate to other platform that Windows, this project need to migrate from .NET Framework to .NET.

Additional context
The only dependency that is not compatible is Sharpshell (the port is still in progress dwmkerr/sharpshell#331).
There is two way of porting File Converter to .NET:

• Continue the work on Sharpshell PR in order to finish it, then port File Converter
• Remove the SharpShell dependency, for example by developping the FileConverterExtension in C++.

Microsoft seems to prefer not having managed extension so the real solution may be to rewrite the extension in C++. This may also with this issue: #211

Porting File Converter to .NET will allow port like Linux or Max port: #370