fix(VTreeview): merge itemProps and activatorProps on VTreeviewGroup's activator

[x-wink]

Description

fixed #21891

Markup:

<template>
  <v-app>
    <v-container>
      <!-- -->
      <VTreeview :items="items" open-on-click />
    </v-container>
  </v-app>
</template>

<script setup lang="ts">
  import { VTreeview } from '@/components';
  const props = {
    class: 'red',
    style: 'color: blue',
  }
  const items = [
    {
      id: 1,
      title: 'Item 1',
      props,
      children: [
        {
          id: '1-1',
          title: 'Item 1.1',
          props,
        },
      ],
    },
    {
      id: 2,
      title: 'Item 1.1',
      props,
    },
  ]
</script>
<style>
.red {
  background: red;
}
</style>