Use abortcontroller to simplify connectedCallback

Per https://github.com/github/auto-complete-element/pull/53#discussion_r761014561, we register many event handlers like `addEventlistener('foo', this.bar = this.bar.bind(bar))`, but rather than calling function bind we can use `handleEvent` and rather than calling `removeEventListener` a bunch, we can store an abort controller per-instance (e.g. with a private field) and abort during `disconnectedCallback`.

The pattern would look as follows:

```ts
class MyElement extends HTMElement {
#ctl = new AbortController()

connectedCallback() {
this.input.addEventListener('foo', this, { signal: this.#ctl.signal })
// many more events here...
}

handleEvent(event) {
if (event.type === 'foo' && event.currentTarget === this.input) {
// do things
}
}

disconnectedCallback() {
this.#ctl.abort()
}

}
```