Upgrade sharpie to use .NET instead of Mono

[rolfbjarne]

Upgrade sharpie to use .NET instead of Mono.

This also means moving away from sharpie's current clang integration to something else, probably https://github.com/dotnet/clangsharp.

[rolfbjarne]

The first version of the new sharpie has been released: https://github.com/dotnet/macios/releases/tag/sharpie-26.3.0.11