Add Syntax Aware Code Folder (when available)

[TravisEz13]

from the VS Code release notes

Folding Provider API
To enable extensions to provide language aware folding ranges, a new provider API is proposed:

export namespace languages {
 /**
   * Register a folding provider.
   *
   * Multiple folding can be registered for a language. In that case providers are sorted
   * by their [score](#languages.match) and the best-matching provider is used. Failure
   * of the selected provider will cause a failure of the whole operation.
   *
   * @param selector A selector that defines the documents this provider is applicable to.
   * @param provider A folding provider.
   * @return A [disposable](#Disposable) that unregisters this provider when being disposed.
   */
 export function registerFoldingProvider(selector: DocumentSelector, provider: FoldingProvider): Disposable;
}

See the full APIs here.
The equivalent APIs are proposed here as protocol extensions to the language server protocol. Feedback is welcome!

[TylerLeonhardt]

Thanks Travis! We'll be watching for this to make it to prime time for us to use.

[TylerLeonhardt]

duping this to #1336