fix(VAutocomplete): selected text is wrong

[tibnor]

Description

The PR fixes two bugs:

Bug: when using items objects the text shown when selecting an item was the item-value and not the item-title. Bug: when focusing VAutocomplete after having selected an item, the text value was set to item-value and not the item-title.

Motivation and Context

How Has This Been Tested?

Visually

Markup:

https://codepen.io/tibnor/pen/KKQqRGz

<template>
  <v-autocomplete v-model="selectedKey" :items="items" item-title="name" item-value="key" />
  <v-autocomplete v-model="selectedKey" :items="itemsRaw" />
</template>

<script>

  export default {
    name: 'Playground',
    data: () => ({
      selectedKey: 1,
      items: [{ name: 'foo', key: 1 }, { name: 'bar', key: 2 }],
      itemsRaw: [{ title: 'foo', value: 1 }, { title: 'bar', value: 2 }],
    }),
  }
</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)