Add an `eventListenerOptions` decorator

[justinfagnani]

lit/lit#531 adds support for declarative event listener options. We should support this with a decorator:

class MyElement extends LitElement {
  render() {
    return html`<button @click=${this.onClick}>Click Me</button>`;
  }

  @eventListenerOptions({capture: true})
  onClick(e) {
    console.log('clicked');
  }
}

We should also document that without decorators, users can simply set an attribute on the method directly:

MyElement.prototype.capture = true;

[jolleekin]

What if the event listener is overridden?

[justinfagnani]

@jolleekin the override will need its own options. We're not going to read from up the prototype chain.

[aadamsx]

@justinfagnani what do you mean by this?

We're not going to read from up the prototype chain.

[frankiefu]

Fixed by #244