feat(VSelect/VAutocomplete/VCombobox): allow persistent menu

[J-Sek]

• allows keeping menu open when multiple is false

closes #20590

<template>
  <v-app theme="dark">
    <v-container width="300">
      <v-combobox
        :items="colors"
        variant="solo"
        _multiple
        density="compact"
        autocomplete="off"
        chips
        closable-chips
        :menu-props="{ offset: 8, closeOnContentClick: false }"
        :list-props="{ density: 'compact', class: 'pa-1 pt-0 border rounded-lg' }"
      >
        <template v-slot:item="{ props }">
          <v-list-item v-bind="props" min-height="32" class="mt-1 rounded">
            <template #append="{ isSelected }">
              <v-checkbox-btn
                class="my-n2 mr-n3"
                style="zoom: 0.8125"
                true-icon="$complete"
                false-icon=""
                :model-value="isSelected"
                @click.prevent
                tabindex="-1"
              />
            </template>
          </v-list-item>
        </template>
      </v-combobox>
    </v-container>
  </v-app>
</template>

<script setup>
  const colors = ['green', 'purple', 'indigo', 'cyan', 'teal', 'orange']
</script>