fix(validation): set input to invalid using error/errorMessages

[nekosaur]

closes #15209

Description

Motivation and Context

How Has This Been Tested?

Markup:

<template>
  <v-app>
    <VForm>
      <VTextField
        v-model="email"
        label="E-mail"
        :error-messages="emailError"
        :error="!!emailError"
      />
    </VForm>
  </v-app>
</template>

<script>
  import { defineComponent } from 'vue'

  export default defineComponent({
    data: () => ({
      email: '',
      emailError: 'Foo',
    }),
  })
</script>

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Improvement/refactoring (non-breaking change that doesn't add any features but makes things better)

Checklist:

• The PR title is no longer than 64 characters.
• The PR is submitted to the correct branch (master for bug fixes and documentation updates, dev for new features and backwards compatible changes and next for non-backwards compatible changes).
• My code follows the code style of this project.
• I've added relevant changes to the documentation (applies to new features and breaking changes in core library)