Use LibraryImport instead of DllImport in v4

[F1schk0pp]

Hi @soukoku and thanks a lot for your effort into NTwain.

Beginning with .NET 7 there is a SourceGenerator for P/Invokes.

https://learn.microsoft.com/en-us/dotnet/standard/native-interop/pinvoke-source-generation

It might be a good thing to use this in v4.

What's your opinion about this?

[Eugene Wang]

That is interesting. I'll see what I can do.