[core] better jsdoc support PROPERTIES

[thepassle]

class MyElement extends HTMLElement {
  /**
   * @type {string} - description
   */
  prop = 'foo';

  constructor() {
    super();
    /** @type {number} - description */ // if duplicate description/type, overwrite the description/type above
    this.prop = 'foo';
  }
}

• [ ] Add docs
• [ ] If jsdoc is applied twice, make the jsdoc in the constructor the override
• [x] Deal with jsdoc type imports ${import('./module.js').SomeType}. Get type SomeType, add reference to ./module.js
• [ ] merge or override with JSDoc declared above the class

[thepassle]

implemented in https://github.com/open-wc/custom-elements-json/pull/27