[core] better JSDoc support

[thepassle]

• [ ] Support jsdoc description/summary for everything
• [ ] Support jsdoc for class field, or default setting stuff in the constructor
• [ ] Deal with jsdoc type imports, e.g. {import('foo').SomeType}

/**
 * Size of the text field
 * @attr
 * @type {"small"|"large"}
 */
size = "large";

constructor() {
  super();
  /**
   * Size of the text field
   * @attr
   * @type {"small"|"large"}
   */
  this.size = "large";
}

  static get observedAttributes() {
    return [
    /** some jsdoc */
    "placeholder",
    /** more jsdoc */
    "disabled",
    ];
  }

/**
 * Dispatched when the enter key is pressed
 */
this.dispatchEvent(new CustomEvent('enter'));

[thepassle]

closing in favor of more refined issues #18 #20 #21 #22 #23