fix(VDataTable): preserve defaults by setting root: true

[prestonyford]

Description

fixes #21814
Fixes contextual defaults for components inside of VMenus that are inside VDataTables. Currently, components that are inside these such as VList and VButton do not properly get their defaults that are defined in the defaults property of Vuetify's configuration object.

Changes

• Added { root: true } when VDataTable provides defaults

Markup:

In my local development environment I set my defaults to:

VDataTable: {
  VMenu: {
    VBtn: {
      density: 'compact',
      variant: 'outlined'
    },
    VList: {
      density: 'compact',
      VBtn: {
        variant: 'plain'
      }
    }
  }
}

And my playground:

<template>
  <v-app>
    <v-data-table :items="[{ name: 'name1', please: 'Click me' }, { name: 'name2', please: 'Click me' }]"
      :disable-sort="true">
      <template v-slot:item="{ index, item }">
        <tr>
          <td>{{ item.name }}</td>
          <td>
            <v-menu>
              <template v-slot:activator="{ props }">
                <v-btn v-bind="props">{{ item.please }}</v-btn>
              </template>
              <v-list>
                <v-list-item>
                  <v-btn>ListButton 1</v-btn>
                  <v-btn>ListButton 2</v-btn>
                </v-list-item>
              </v-list>
            </v-menu>
          </td>
        </tr>
      </template>
    </v-data-table>
  </v-app>
</template>

<script>
export default {
  name: 'Playground',
  setup() {
    return {
      //
    }
  },
  data() {
    return {
    }
  }
}
</script>