feat(VFileInput): update to v3

[nekosaur]

Fixes #9349

Description

Motivation and Context

v3

How Has This Been Tested?

Markup:

<template>
  <v-app>
    <div class="pa-10">
      <h3>Variants</h3>
      <template v-for="variant in ['underlined', 'outlined', 'filled', 'contained', 'plain']" :key="variant">
        <v-file-input :label="variant" :variant="variant" class="ma-5" />
      </template>

      <h3>Multiple</h3>
      <v-file-input label="bar" multiple class="ma-5" />

      <h3>Multiple Counter</h3>
      <v-file-input label="bar" multiple counter class="ma-5" />

      <h3>Multiple Counter ShowSize</h3>
      <v-file-input label="bar" multiple counter show-size class="ma-5" />

      <h3>Not Clearable</h3>
      <v-file-input label="bar" :clearable="false" class="ma-5" />

      <h3>No prepend icon</h3>
      <v-file-input label="bar" :prepend-outer-icon="null" class="ma-5" />

      <h3>Programmatic</h3>
      <v-file-input label="bar" v-model="file" class="ma-5" />
      {{ file }}
      <v-btn @click="set">set</v-btn>
      <v-btn @click="clear">clear</v-btn>
    </div>
  </v-app>
</template>

<script>
  export default {
    name: 'Playground',
    data: () => ({
      model: 1,
      disabled: false,
      file: null,
      toSet: null,
    }),
    watch: {
      file (value) {
        value && value.length && (this.toSet = value)
      },
    },
    methods: {
      set () {
        this.file = this.toSet
      },
      clear () {
        this.file = []
      },
    },
  }
</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)

[KaelWD]

Update to the new webpack-dev-server schema

[johnleider]

I wasn't able to find any information regarding this in webpack-dev-server@3.x, only 4.0-rc. Could you clarify this?