element 动态渲染form表单，添加验证

要点  :prop="`subAccountList[${index}].companyName`"

   <div
        class="form-block son-unit_form"
        v-for="(item, index) in form.subAccountList"
        :key="index"
      >
        <div class="del-icon" @click="clickDeleteSonUnit(item, index)">
          <el-button
            type="info"
            icon="el-icon-close"
            size="mini"
            circle
          >el-button>
        div>
        <el-form-item
          :label="`子单位${index + 1}`"
          :prop="`subAccountList[${index}].companyName`"
          :rules="[
            {
              required: true,
              message: `请输入子单位${index + 1}名称`,
              trigger: 'blur',
            },
            {
              min: 1,
              max: 30,
              message: '单位名称不允许超过30个字',
              trigger: ['blur', 'change'],
            },
          ]"
        >
          <el-input
            v-model="item.companyName"
            clearable
            maxlength="30"
            placeholder="请输入可作为发票抬头的单位名称"
          >el-input>
        el-form-item>
        <el-form-item label="纳税人识别号">
          <el-input
            v-model="item.taxpayerNumber"
            clearable
            maxlength="20"
            placeholder="请输入纳税人识别号(20位数字或字母)"
          >el-input>
        el-form-item>
        <el-form-item label="开户行:">
          <el-input
            v-model="item.bankName"
            clearable
            maxlength="10"
            placeholder="请输入开户行(建议精确到分行或支行)"
          >el-input>
        el-form-item>
        <el-form-item label="银行卡号:">
          <el-input
            v-model="item.bankCardNo"
            clearable
            maxlength="20"
            placeholder="请输入开银行卡号(20位以内的数字)"
          >el-input>
        el-form-item>
        <el-form-item label="电话:">
          <el-input
            v-model="item.invoicePhoneNumber"
            clearable
            maxlength="12"
            placeholder="请输入电话"
          >el-input>
        el-form-item>
        <el-form-item label="地址:">
          <el-input
            v-model="item.invoiceAddress"
            maxlength="100"
            :autosize="{ minRows: 1, maxRows: 4 }"
            type="textarea"
            placeholder="请输入地址"
          >el-input>
        el-form-item>
        <el-form-item>el-form-item>
      div>