fix(validation): validate initial input value

[nekosaur]

Description

closes #15568

this is a change to default behaviour, but I think the old behaviour could be classified as a bug.

Markup:

<template>
  <v-form v-model="valid">
    <v-text-field autofocus label="name" v-model="name" required :rules="nameRules"></v-text-field>
    <v-text-field label="type" v-model="type" required :rules="typeRules"></v-text-field>
  </v-form>
  Valid: {{ valid === null ? 'null' : valid }}
  <v-btn :disabled="!valid">Sa</v-btn>
</template>

<script>

  export default {
    data () {
      return {
        valid: false,
        name: '',
        type: 'asdasdasdasd',
        nameRules: [(v) => (!!v && v.length > 5) || "EDITOR.stories.storyNameRequired"],
        typeRules: [(v) => !!v || "EDITOR.stories.typeIsRequired"],
      }
    },
  }
</script>

[nekosaur]

TODO: this has the same issue as optional PR in that empty value is different for different components so just checking if(model.value) is probably not enough

[johnleider]

TODO: this has the same issue as optional PR in that empty value is different for different components so just checking if(model.value) is probably not enough

What about a clearFunction property that each component would define?

[KaelWD]

This should be more similar to v2.

• Inputs should always be validated initially no matter what the value is
• There should be some way to run validation "silently" without displaying errors to the user
• There should be some way to disable the initial validation, for example if async rules are used