fix(VCombobox/VAutocomplete): Only allow input to completely overlap selection when focused

[yuwu9145]

fixes #18796

Description

Markup:

<template>
  <v-app>
    <v-container>
      <v-autocomplete
        chips
        v-model="state"
        closable-chips
        label="Autocomplete"
        :items="['California', 'Colorado', 'Florida', 'Georgia', 'Texas', 'Wyoming']"
      ></v-autocomplete>
      <v-combobox
        chips
        closable-chips
        v-model="state"
        label="Combobox"
        :items="['California', 'Colorado', 'Florida', 'Georgia', 'Texas', 'Wyoming']"
      />
      <v-select
        chips
        closable-chips
        v-model="state"
        label="Select"
        :items="['California', 'Colorado', 'Florida', 'Georgia', 'Texas', 'Wyoming']"
      />
    </v-container>
  </v-app>
</template>

<script setup>
  import { ref } from 'vue'

  const state = ref('California')
</script>