Added language service support for auto-completion and semantic token

[veler]

Pull request type

Please check the type of change your PR introduces:

• Bugfix
• New feature or enhancement
• UI change (please include screenshot!)
• Code style update (formatting, renaming)
• Refactoring (no functional changes, no api changes)
• Build related changes
• Documentation content changes
• Internationalization and localization
• Other (please describe):

What is the current behavior?

There's no way to have a custom language support using Monaco Editor in DevToys.

What is the new behavior?

Added a Language Service API that reflects the one of Monaco Editor (but simplified and abstracted as much as possible). Specifically, auto-completion and semantic colorization is supported.

Other information

To use it, in a DevToys extension:

[Export(typeof(ILanguageService))]
[Name("my-language")]
internal sealed class MyLanguageService : ILanguageService
{
    public async Task<IReadOnlyList<AutoCompletionItem>> GetAutoCompletionItemsAsync(string textDocument, TextSpan span, CancellationToken cancellationToken)
    {
        // TODO
    }
    
    public async Task<IReadOnlyList<SemanticToken>> GetSemanticTokensAsync(string textDocument, CancellationToken cancellationToken)
    {
        // TODO
    }
}

// And then, in a IGuiTool:

MultiLineTextInput().Language("my-language")

Here is how things can look like when implementing these methods:

Quality check

Before creating this PR:

• Did you follow the code style guideline as described in CONTRIBUTING.md
• Did you build the app and test your changes?
• Did you check for accessibility? On Windows, you can use Accessibility Insights for this.
• Did you verify that the change work in Release build configuration
• Did you verify that all unit tests pass
• Tested manually with a sample extension.
• If necessary and if possible, did you verify your changes on:
  • Windows
  • macOS
  • Linux