Fix/#11989 autocomplete focus

[YipingRuan]

fix #11989
fix #12031 (The wrong fix)

Description

Copied idea from VTextField

Motivation and Context

How Has This Been Tested?

Markup:

<template>
  <div id="app">
    <v-app>
      <div style="width: 200px; margin: auto;">
        <v-autocomplete
          ref="autocomplete"
          v-model="model"
          :items="items"
        ></v-autocomplete>
        <v-btn @click.stop="focusAutocomplete">focus</v-btn>
        <v-text-field
          ref="textfield"
          v-model="model"
        ></v-text-field>
        <v-btn @click.stop="focusTextField">focus</v-btn>
        <v-select :items="items"></v-select>
      </div>
    </v-app></div>

</template>

<script>
  export default {
    data: () => ({
      model: null,
      items: [
        'Autocompletes', 'Comboboxes', 'Forms', 'Inputs', 'Overflow Buttons', 'Selects', 'Selection Controls', 'Sliders', 'Textareas', 'Text Fields',
      ],
    }),
    computed: {
      dateRangeText () {
        return this.dates.join(' ~ ')
      },
    },
    methods: {
      focusAutocomplete () {
        this.$refs.autocomplete.focus()
      },
      focusTextField () {
        this.$refs.textfield.focus()
      },
    },
  }
</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)

[johnleider]

Requesting Final comments from @vuetifyjs/contributors @vuetifyjs/core-team