Add `id` to error entries for iteration

It is considered the best practice in Vue.js to define key for v-for iterations for performance and determinism reasons. And it is not uncommon to use vuelidate results this way:

  <div class="input-errors" v-for="error of state.v$.classifierId.$errors" v-bind:key="error ">
    <div class="error-msg">{{ error.$message }}</div>
  </div>

However, currently there is no unique id exposed on error array that could be used for v-bind: key, and generic error has to be used, which is against the Vue.js recommendation.

To Reproduce Perform any validation that results in errors.

Expected behavior There is a unique id field per entry in $errors array.

[dobromir-hristov]

PR is up, @shentao will review when he gets some time and we can release it 😃

[kibertoad]

Yup, that would definitely work!