fix(VFileInput): use internalArrayValue

[MajesticPotatoe]

Description

Fix for v-file-input error: this.internalValue.forEach is not a function when using selection slot without the multiple prop

Motivation and Context

fixes #8351

How Has This Been Tested?

visually

Markup:

<template>
  <v-container grid-list-md>
    <v-file-input
      v-model="files"
      label="Single File"
      placeholder="Select File"
      outlined
    >
      <template v-slot:selection="{ text }">
        <v-chip
          label
          small
        >
          {{ text }}
        </v-chip>
      </template>
    </v-file-input>
    <v-file-input
      v-model="filesMultiple"
      label="Multiple Files"
      placeholder="Select Files"
      outlined
      multiple
    >
      <template v-slot:selection="{ text }">
        <v-chip
          label
          small
        >
          {{ text }}
        </v-chip>
      </template>
    </v-file-input>
  </v-container>
</template>

<script>
  export default {
    data: () => ({
      files: null,
      filesMultiple: [],
    }),
  }
</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 breaking 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)
• I've added new examples to the kitchen (applies to new features and breaking changes in core library)