Support slnx solution format

[mom-bbtsoftware]

Is your feature request related to a problem? Please describe.
We have started to convert all our solutions to the (more short and simple) new slnx format.

See: https://devblogs.microsoft.com/dotnet/introducing-slnx-support-dotnet-cli/
The feature is now in production with the latest visual studio / dot net sdk 9.0.200+ (has left the preview state).

With slnx, currently the codeconverter vs plugin stops with an expection, that doesnt tell the exact reason. When trying with the console version, we get a message regarding only "sln" is possible.

Describe the solution you'd like
Support slnx.

Describe alternatives you've considered
Currently we had to migrate the solutions back to sln to make the converter work again, wich is a bit of a pain, because the sln is much more specific about project types and configurations.

[GrahamTheCoder]

Yep thanks for raising this. Happy to help with a PR from anyone but I'm unlikely to work on it solo due to time constraints.
With this and general VS2026 support the main challenge will be balancing:

• New libraries required for new features
• Old libraries to allows old VS versions - which are needed to load older legacy VB apps people are converting
  Some conditional compilation may be necessary to satisfy both