fix:(VDataTable): Slots for tbody and thead not overriding default tags

[codetakki]

Fixes #18854 where tbody slot does not replace the default tbody

Description

The tbody slot was placed after the tbody tag, resulting in the slot just being appended to the body.
Trying to add any custom tbody inside the body slot results in broken styling, making it harder to customize tables.
It seems to have worked as expected in v2, if understanding this Stackoverflow comment correctly

Markup

<template>
  <div>
    <v-data-table
      :headers="headers"
      :items="items"
      :items-per-page="-1"
      item-key="name"
    >
      <template #thead>
        <thead>
          <tr>
            <th>
              Name
            </th>
            <th>
              Sport
            </th>
            <th>
              ID
            </th>
          </tr>
        </thead>
      </template>
      <template #tbody>
        <tbody>
          <tr
            v-for="item in items"
            :key="item.name"
          >
            <td v-for="header in headers" :key="header">{{ item[header.value] }}</td>
          </tr>
        </tbody>
      </template>
    </v-data-table>
  </div>

</template>
<script>

  export default {
    data () {
      return {
        items: [
          { id: 1, name: 'Abby', sport: 'basket' },
          { id: 2, name: 'Brooke', sport: 'foot' },
          { id: 3, name: 'Courtenay', sport: 'volley' },
          { id: 4, name: 'David', sport: 'rugby' },
          { id: 5, name: 'Emma', sport: 'tennis' },
          { id: 6, name: 'Finn', sport: 'soccer' },
          { id: 7, name: 'Grace', sport: 'swimming' },
          { id: 8, name: 'Henry', sport: 'baseball' },
          { id: 9, name: 'Isaac', sport: 'hockey' },
          { id: 10, name: 'Jasmine', sport: 'badminton' },
          { id: 11, name: 'Kai', sport: 'cricket' },
          { id: 12, name: 'Liam', sport: 'golf' },
          { id: 13, name: 'Mia', sport: 'surfing' },
          { id: 14, name: 'Noah', sport: 'skiing' },
          { id: 15, name: 'Olivia', sport: 'snowboarding' },
          { id: 16, name: 'Peyton', sport: 'cycling' },
          { id: 17, name: 'Quinn', sport: 'running' },
          { id: 18, name: 'Ryan', sport: 'wrestling' },
          { id: 19, name: 'Sophia', sport: 'boxing' },
          { id: 20, name: 'Tyler', sport: 'surfing' },
        ],
        headers: [
          {
            title: 'Name',
            value: 'name',
          },
          {
            title: 'sport',
            value: 'sport',
          },
          {
            title: 'id',
            value: 'id',
          },
        ],
      }
    },
  }
</script>

[KaelWD]

#17206 (comment)