fix(VDataTableVirtual): correct item selection when shift-clicking

[hdJerry]

Summary

Fixes an issue where VDataTableVirtual selected the wrong range of items when holding Shift while the table was sorted by a specific column.

Fix

Used the actual index based on the item position in the array and not the index in the item itself

<template>
  <v-app>
    <v-main>
      <v-container>
        <v-card>
          <v-data-table-virtual
            v-model="selected"
            :headers="headers"
            :items="items"
            :sort-by="[{ key: 'name', order: 'asc' }]"
            item-value="id"
            show-select
            height="400"
          />
          <v-card-text> <b>Selected IDs:</b> {{ selected }} </v-card-text>
        </v-card>
      </v-container>
    </v-main>
  </v-app>
</template>

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


  const selected = ref([])

  const headers = [
    { title: 'ID', value: 'id', width: '100px' },
    { title: 'Name', value: 'name' },
  ]

  // A simple dataset
  const items = Array.from({ length: 100 }, (_, i) => ({
    id: i + 1, // Unique ID
    name: `User ${i + 1}`,
  }))
</script>

Closes #22220