Recognize properties introduced by jQuery extend

The old VS JS language service used to make runtime types available at design-time, allowing it to support jQuery's extend function for adding properties dynamically. The new one uses static types and so does not offer these symbols during completion, navigate-to, etc. We've had some customer inquiries about the possibility of supporting this functionality in the TS language service.

https://developercommunity.visualstudio.com/content/problem/529989/aspnet-在html-文件-js-智能提示失效.html
https://developercommunity.visualstudio.com/content/problem/560277/javascript-go-to-members-doesnt-work-with-property.html

The latter provided this example:

(function ($) {

    mynamespace.myClass = Class.extend({
      init: function (options) {
        // unless you specifically type this.testProperty = "abc" in JS, the 'Go to Members' will not find the below property even though it's explicitely defined.
      },
       __properties: {

       'testProperty': {
                /// <summary>
                /// Gets or sets the test property
                /// </summary>
                /// <value type="String"></value>

                get: function () {
                    return this._testProperty;
                },

                set: function (value) {
                    this._testProperty = value;
                }
            }
       }
   });

})(jQuery);

まず、リンクされている2件の Developer Community レポートと jQuery/Class.extend の例を確認します。ソースファイルやテストは指定されていないため、最初に completion と navigate-to のための TypeScript language-service のエントリポイントを特定し、そのうえで動的に導入されたプロパティの認識が対象とすべき範囲と、テスト方法を定義します。