[element-ui] el-tabs的标题使用el-dropdown

<el-tabs v-model="activeTab">
  <el-tab-pane>
    <template #label>
      <el-dropdown trigger="click" @command="handleDropdownCommand">
        <span class="dropdown-title">{{ dropdownTitle }}</span>
        <i class="el-icon-arrow-down el-icon--right"></i>
        <el-dropdown-menu slot="dropdown">
          <el-dropdown-item command="option1">Option 1</el-dropdown-item>
          <el-dropdown-item command="option2">Option 2</el-dropdown-item>
        </el-dropdown-menu>
      </el-dropdown>
    </template>
    <!-- 内容 -->
  </el-tab-pane>
</el-tabs>

data() {
  return {
    activeTab: '0', // 当前激活的选项卡的索引
    dropdownTitle: 'Default Title' // 下拉标题
  };
},
methods: {
  handleDropdownCommand(command) {
    this.dropdownTitle = command; // 更换下拉标题为选中的选项
  }
}