Listbox onOpen event for purpose of scrolling selected option into view

[vincerubinetti]

Related to #975

I don't believe the current options allow for this conveniently. It'd be nice to have some events like onOpen and onClose, in case we need to do side effects like this.

This is my current workaround, which I don't like:

<template>
  <ListboxOption
    v-for="option in options"
    v-slot="{ active, selected }"
    :key="option.id"
    as="template"
    :value="option"
  >
    <li
      :class="{ active, selected }"
      @vnode-mounted="(node: VNode) => selected && onOpen(node)"
    >
      blah
    </li>
  </ListboxOption>
</template>

<script setup lang="ts">
// when listbox opened
async function onOpen(node: VNode) {
  await frame();
  (node.el as Element).scrollIntoView();
}
</script>

You may want to add scrollIntoView as default behavior, or at least an option. It's really necessary for long lists of options.