fix(VVirtualScroll): call calculateVisibleItems after updateOffsets

[pinichi]

Description

resolves #22937

When handleItemResize is called (e.g. after an accordion-like collapse), it triggers the debounced updateOffsets() which correctly rebuilds offsets[].

However, calculateVisibleItems() was never called afterwards, leaving paddingBottom stale until the next scroll event — causing the scrollbar to display an incorrect size.

Markup:

<template>
  <div style="max-width: 600px; margin: 0 auto; padding: 16px">
    <div style="margin: 12px 0; line-height: 2">
      <div>50 items × 48px → item #0 collapses to 12px</div>
      <div>Expected paddingBottom after collapse: <b>~300px</b></div>
      <div>
        Actual paddingBottom:
        <b :style="{ color: paddingBottom !== null && paddingBottom > 800 ? 'red' : 'green' }">
          {{ paddingBottom !== null ? paddingBottom + 'px' : '(click Collapse)' }}
        </b>
        <span v-if="paddingBottom !== null && paddingBottom > 800" style="color: red; font-weight: bold">
          ← stale! (bug)
        </span>
        <span v-else-if="paddingBottom !== null" style="color: green"> ✓ correct</span>
      </div>
    </div>

    <div style="display: flex; gap: 8px; margin-bottom: 12px">
      <button @click="collapse" :disabled="collapsed">Collapse item #0</button>
      <button @click="reset">Reset</button>
    </div>

    <div style="margin-bottom: 8px; font-size: 12px; color: #555">
      <div>👉 1. Click "Collapse item #0" — do NOT scroll</div>
      <div>　　2. paddingBottom stays ~1200px (bug)</div>
      <div>　　3. Scroll slightly → paddingBottom corrects to ~300px</div>
    </div>

    <v-virtual-scroll ref="vsRef" :items="items" height="400">
      <template #default="{ index }">
        <div :style="{ height: index === 0 && collapsed ? '12px' : '48px' }">
          #{{ index }} — {{ index === 0 && collapsed ? '12px (collapsed)' : '48px' }}
        </div>
      </template>
    </v-virtual-scroll>
  </div>
</template>

<script setup>
import { ref } from 'vue'

const items = Array.from({ length: 50 }, (_, i) => i)
const collapsed = ref(false)
const vsRef = ref(null)
const paddingBottom = ref(null)

async function collapse() {
  collapsed.value = true
  await new Promise(resolve => setTimeout(resolve, 500))
  const container = vsRef.value?.$el?.querySelector('.v-virtual-scroll__container')
  paddingBottom.value = parseFloat(container?.style.paddingBottom ?? '0')
}

function reset() {
  collapsed.value = false
  paddingBottom.value = null
}
</script>