Expose API for getting JSDoc nodes in TypeScript files

Closure adds various semantic JSDoc annotations that aren't currently modeled by TypeScript, such as @export (unrelated to TS export) and @nosideeffects.
https://developers.google.com/closure/compiler/docs/js-for-compiler#overview

As part of our tool chain to run TypeScript through Closure we'd like to be able to munge these via the TypeScript API. It appears TypeScript gathers JSDoc comments when parsing JavaScript -- is there a good reason to not gather these in TypeScript as well?

Specifically, I believe my suggestion amounts to removing the "if" statement in the below code (though I'm not certain this is the right place) in parser.ts:

        function addJSDocComment<T extends Node>(node: T): T {
            if (contextFlags & NodeFlags.JavaScriptFile) {
                ...all of the code is in here...
            }
        }

从 parser.ts 中的 addJSDocComment 开始，检查 NodeFlags.JavaScriptFile 守卫如何限制 JSDoc 的收集。将现有的 JavaScript 解析路径与 TypeScript 文件解析进行比较，并查看 issue 讨论以了解预期的 API 边界。当可以通过 TypeScript API 访问 TypeScript 文件的 JSDoc 节点（包括 @export 和 @nosideeffects 等 Closure 注解）时，即表示完成。