fix(VAutocomplete): keyboard navigation with virtual scroll items

[hellozzm]

Summary

When using VAutocomplete with many items (e.g., 100+), keyboard navigation with ArrowUp/ArrowDown only works through the currently visible items in the virtual scroll. This is because VList's focusChild function filters out non-rendered DOM elements via offsetParent check, so items outside the viewport are not navigable.

This fix intercepts ArrowUp/ArrowDown keydown events in the menu handler, tracks the current virtual list index, uses VVirtualScroll.scrollToIndex() to scroll to the target item, and then focuses it.

Playground Markup

<template>
  <v-app>
    <v-container style="max-width: 400px">
      <v-autocomplete
        label="Select an item"
        :items="items"
        density="comfortable"
      ></v-autocomplete>
    </v-container>
  </v-app>
</template>

<script setup>
  const items = Array.from({ length: 100 }, (_, i) => `Item ${i + 1}`)
</script>

Testing

1. Open the playground above
2. Click on the autocomplete to open the dropdown
3. Press ArrowDown repeatedly - should navigate through ALL 100 items, scrolling as needed
4. Press ArrowUp at the first item - should wrap to the last item
5. Press ArrowDown at the last item - should wrap to the first item
6. Expected: smooth navigation through all items with proper scroll behavior
7. Before fix: navigation would only cycle through visible items (~10-15)

Fixes #22770

[J-Sek]

Please stop posting AI slop. There is nothing of value in this PR