[WIP] VS for Windows language extension compatibility test

[lextm]

This is not a pull request that aim to be thoroughly reviewed or merged, because I use Claude to produce it for just a few evaluation goals,

• If SharpIDE can have a TextMate based highlighting engine. That would enable a lot of programming languages to be supported quickly.
• If an existing VS for Windows language extension can be brought even without any modifications. The example I choose is this one for T4, a very simple .vsix with just a TextMate syntax file.

If this simple test case can pass, then we can move on to experiment with language server (which many more modern language extensions use), and even deeper integration with a VS for Windows compatible extensibility SDK.

Of course, it revealed many gaps (like current tight/direct integration with Roslyn, not over the standard language server protocol). That's why such experiments are important even before 1.0 is shipped.

I agree to the terms of contributing as stated here

[lextm]

Extend the .vsix import to work for simple VS Code extensions too. One example is this one for reStructuredText.

[lextm]

Svelte language support from VS for Windows can be imported with highlighting and completion.