fix(groups): use suspense to delay rendering of group items

[KaelWD]

fixes #15207

Probably need the same for #15202 - collect all the items before rendering anything

An alternative would be to keep values instead of ids, and do a deepEqual on demand like in v2. That wouldn't help with #15202 though because layout items all depend on each other.

<template>
  <v-app>
    <v-container>
      <v-card>
        <v-btn-toggle v-model="selected" multiple variant="outlined">
          <v-btn v-for="server in items" :key="server">
            Server {{ server }}
          </v-btn>
        </v-btn-toggle>
        <br>
        You select: {{ selected }}
      </v-card>

      <v-card>
        <v-tabs>
          <v-tab>One</v-tab>
          <v-tab>Two</v-tab>
          <v-tab>Three</v-tab>
        </v-tabs>
      </v-card>

      <v-item-group>
        <v-item>
          <div>a</div>
          <div>b</div>
        </v-item>
      </v-item-group>

    </v-container>
  </v-app>
</template>

<script setup>
  import { computed, ref, watch } from 'vue'

  const items = [0, 1, 2]
  const selected = ref([...items])
</script>