fix(VFileInput): on drop internal input unpopulated (#21248)

[jcjp]

Description

• Fixes: [Bug Report][3.8.1] VFileInput - Underlying <input> not populated when file is dragged into component #21248

---

• On file drop on VFileInput component the internal input element files value is unpopulated or not updated
• The issue is also observed on clear, the files value remains even if clear button was clicked and file was removed
• Minor refactor and code cleanup

Markup:

<template>
  <v-app>
    <v-container>
      <v-file-input
        v-model="file"
        ref="fileInput"
        @update:model-value="updateFileList"
      />
      <pre>
Number of files in internal &lt;input&gt; tag = {{ inputFieldFiles }}</pre
      >
    </v-container>
  </v-app>
</template>

<script setup>
import { ref, computed, watch, nextTick } from 'vue'

const file = ref()
const fileInput = ref()

const inputFieldFiles = ref(0)
function updateFileList() {
  inputFieldFiles.value = fileInput.value.files.length
}
</script>

[johnleider]

#21248 actually ended up being fixed by #21182, more specifically dfaece7