fix(VFileInput): prevent label and placeholder overlap

[juddfranklin1]

fixes #12864

Description

Motivation and Context

How Has This Been Tested?

Markup:

<template>
  <v-app>
    <v-container>
      <v-file-input
        accept="image/*"
        label="File input"
        placeholder="placeholder"
      ></v-file-input>
      <v-file-input
        accept="image/*"
        label="File input 2"
      ></v-file-input>
    </v-container>
  </v-app>
</template>

<script>
  export default {
    data: () => ({
    //
    }),
  }
</script>

Types of changes

• [x ] 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:

• [x ] The PR title is no longer than 64 characters.
• [x ] 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).
• [x ] My code follows the code style of this project.
• [x ] I've added relevant changes to the documentation (applies to new features and breaking changes in core library)

[johnleider]

I don't like the idea of adding a property to fix a bug. This should follow the same logic as v-text-field which was altered in ff500ba for a11y concerns.

[juddfranklin1]

I don't like the idea of adding a property to fix a bug. This should follow the same logic as v-text-field which was altered in ff500ba for a11y concerns.

This is helpful, thanks. I was a little uneasy about the approach, but didn't know about the comparable solution in v-text-field