[folding] mode to have region based folding only

<!-- ⚠️⚠️ Do Not Delete This! feature_request_template ⚠️⚠️ --> <!-- Please read our Rules of Conduct: https://opensource.microsoft.com/codeofconduct/ --> <!-- Please search existing issues to avoid creating duplicates. --> <!-- Describe the feature you'd like. --> Is it possible to remove folding for the language, but leave it only for writing keywords (for example in C# #region #endregion)