fix(VCombobox): do not add search to list when selecting items with keyboard

[haggys22]

Description

There was a timing issue with this.$nextTick, triggering the selection twice: once for the selected VMenu item and once for the search term when the menu index is -1.

See #8841 (comment) for the code execution order without this fix.

Motivation and Context

This fixes #8841. Also the workaround for #8842 works again.

How Has This Been Tested?

visually

Markup

<template>
  <v-container>
    <v-combobox
            v-model="model"
            :items="items"
            :search-input.sync="search"
            hide-selected
            label="Add some tags"
            multiple
            persistent-hint
            chips
    ></v-combobox>
  </v-container>
</template>

<script>
export default {
  data: () => ({
    items: ['Gaming', 'Programming', 'Vue', 'Vuetify'],
    model: [],
    search: null,
  }),
  watch: {
    model() {
      this.search = null
    }
  }
}
</script>

Types of changes

• Bugfix (non-breaking change which fixes a bug)
• 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)

[TravisBuddy]

Hey @haggys22,
Your changes look good to me!

View build log

TravisBuddy Request Identifier: c7a9b3c0-3607-11ea-b480-9fec542541c3

[haggys22]

For some reason the test

FAIL Vuetify src/components/VSelect/__tests__/VSelect4.spec.ts
  ● VSelect.ts › should emit listIndex event when navigated by keyboard

    expect(jest.fn()).toHaveBeenCalledWith(expected)

    Expected mock function to have been called with:
      0
    as argument 1, but it was called with
      -1.

fails, but inspecting a VSelect with Vue devtools shows that update:list-index is emitted with the correct index when navigating with the keyboard

[haggys22]

@johnleider

• Updated branch
• Added Playground.vue to PR message
• Fixed failing test
• Updated PR title/message as this does not even fix the issue but only the workaround

[johnleider]

Testing your branch and the issue still persists.

[haggys22]

With my latest changes the v1.5.18 behaviour is restored, i.e. after pressing enter only the selected item is added as a chip and the search term remains in the input field

[johnleider]

Please add a corresponding unit test for this, thank you!

[johnleider]

Determined that #8841 was a duplicate of #6697