fix(VVirtualScroll): invoke handleScroll when items change

[johnleider]

Motivation and Context

fixes #16725

Markup:

<template>
  <VApp>
    <VMain>
      <VSheet class="mx-5">
        <VVirtualScroll :items="items" height="300" :visible-items="10">
          <template #default="{ item, index }">
            <p>
              {{ index + 1 }} - {{ item }}
            </p>
          </template>
        </VVirtualScroll>
        <p class="mt-3">Total: {{ items.length }}</p>
      </VSheet>
    </VMain>
  </VApp>
</template>

<script setup>
  import { onMounted, onUnmounted, ref } from 'vue'

  const items = ref([
    'sentence The rough teacher sadly dodged because some teacher humbly rolled below a rough hamster which, became a dumb, lovely old lady.',
    'The soft hamster elegantly kicked because some old lady proudly died above a vibrating boy which, became a lazy, beautiful clock.',
    'The soft plastic calmly died because some old lady proudly died above a lovely old lady which, became a vibrating, soft hamster.',
    'The professional professor proudly rolled because some boy precisely flew up a hot dog which, became a soft, rough bird.',
    'The vibrating old lady slowly rolled because some hamster calmly slept across a soft teacher which, became a beautiful, rough old lady.',
    'sentence The rough teacher sadly dodged because some teacher humbly rolled below a rough hamster which, became a dumb, lovely old lady.',
    'The soft hamster elegantly kicked because some old lady proudly died above a vibrating boy which, became a lazy, beautiful clock.',
    'The soft plastic calmly died because some old lady proudly died above a lovely old lady which, became a vibrating, soft hamster.',
    'The professional professor proudly rolled because some boy precisely flew up a hot dog which, became a soft, rough bird.',
    'The vibrating old lady slowly rolled because some hamster calmly slept across a soft teacher which, became a beautiful, rough old lady.',
  ])

  const nouns = ['bird', 'clock', 'boy', 'plastic', 'duck', 'teacher', 'old lady', 'professor', 'hamster', 'dog']
  const verbs = ['kicked', 'ran', 'flew', 'dodged', 'sliced', 'rolled', 'died', 'breathed', 'slept', 'killed']
  const adjectives = ['beautiful', 'lazy', 'professional', 'lovely', 'dumb', 'rough', 'soft', 'hot', 'vibrating', 'slimy']
  const adverbs = ['slowly', 'elegantly', 'precisely', 'quickly', 'sadly', 'humbly', 'proudly', 'shockingly', 'calmly', 'passionately']
  const preposition = ['down', 'into', 'up', 'on', 'upon', 'below', 'above', 'through', 'across', 'towards']

  function sentence () {
    const rand1 = Math.floor(Math.random() * 10)
    const rand2 = Math.floor(Math.random() * 10)
    const rand3 = Math.floor(Math.random() * 10)
    const rand4 = Math.floor(Math.random() * 10)
    const rand5 = Math.floor(Math.random() * 10)
    const rand6 = Math.floor(Math.random() * 10)
    return 'The ' + adjectives[rand1] + ' ' + nouns[rand2] + ' ' + adverbs[rand3] + ' ' + verbs[rand4] + ' because some ' + nouns[rand1] + ' ' + adverbs[rand1] + ' ' + verbs[rand1] + ' ' + preposition[rand1] + ' a ' + adjectives[rand2] + ' ' + nouns[rand5] + ' which, became a ' + adjectives[rand3] + ', ' + adjectives[rand4] + ' ' + nouns[rand6] + '.'
  }

  const interval = setInterval(() => {
    // console.log('adding more sentences')
    for (let i = 0; i < 5; i++) {
      items.value.push(sentence())
    }
  }, 2000)

  onUnmounted(() => {
    clearInterval(interval)
  })
</script>

[johnleider]

closing in favor of #16736