fix(VAutocomplete): reset selection index to -1 after deletion

[TIM56887]

Description

fixes #20796
Reset selectionIndex to -1 after using Backspace or Delete

Markup:

<template>
  <v-autocomplete
    :items="['California', 'Colorado', 'Florida', 'Georgia', 'Texas', 'Wyoming']"
    label="Autocomplete"
    multiple
  />
</template>

[babu-ch]

Will I be unable to perform continuous deletions?

[TIM56887]

Hi @babu-ch,

Yes, after this change, it will be unable to perform continuous deletions directly with a single backspace press. But can still delete by pressing backspace twice.