Optional arguments in JSDoc types may be moved to TypeScript types quickfix

<!-- 🚨 STOP 🚨 𝗦𝗧𝗢𝗣 🚨 𝑺𝑻𝑶𝑷 🚨 Half of all issues filed here are duplicates, answered in the FAQ, or not appropriate for the bug tracker. Even if you think you've found a *bug*, please read the FAQ first, especially the Common "Bugs" That Aren't Bugs section! Please help us by doing the following steps before logging an issue: * Search: https://github.com/Microsoft/TypeScript/search?type=Issues * Read the FAQ: https://github.com/Microsoft/TypeScript/wiki/FAQ Please fill in the *entire* template below. --> <!-- Please try to reproduce the issue with `typescript@next`. It may have already been fixed. --> **TypeScript Version:** 3.4.3 <!-- Search terms you tried before logging this (so others can find this issue more easily) --> - `80004` - `jsdoc quickfix optional` **Code** With Closure Compiler, you mark a function parameter optional by adding an `=` after its type ([reference][2]): ```ts /** * @param a {string} Base string. * @param b {string=} Optional string to add * @return {string} */ function foo(a, b) { if (b) return a + b; return a; } ``` TypeScript offers a quickfix to convert these jsdoc annotations to TypeScript types:  **Expected behavior:** The `b` parameter should be optional: ```ts /** * @param a {string} Base string. * @param b {string=} Optional string to add * @return {string} */ function foo(a: string, b?: string): string { if (b) return a + b; return a; } ``` **Actual behavior:** The `b` parameter is required but has type `string | optional`: ```ts /** * @param a {string} Base string. * @param b {string=} Optional string to add * @return {string} */ function foo(a: string, b: string | undefined): string { if (b) return a + b; return a; } ``` This means that all calls of the function which don't specify `b` will be flagged as errors. **Playground Link:** <!-- A link to a TypeScript Playground "Share" link …