feat(VSelect): Add list-header slot

[Haviles04]

resolves #22400

Markup

<template>
  <v-app theme="dark">
    <v-container class="d-flex align-center ga-3" max-width="600">
      <v-toolbar>
        <div class="d-flex ga-3 justify-space-evenly w-100">
          <v-switch v-model="headerEnabled" label="header" hide-details />
          <v-switch v-model="footerEnabled" label="footer" hide-details />
          <v-switch v-model="forceNoData" label="no-data" hide-details />
        </div>
      </v-toolbar>
    </v-container>

    <v-container class="d-flex align-center ga-3" max-width="600">
      <v-btn text="btn before" />
      <v-select
        v-model="selectedItems"
        v-model:menu="menu1"
        :items="forceNoData ? [] : items"
        class="rounded-lg"
        item-title="value"
        label="header + footer"
        hide-details
        multiple
      >
        <template v-if="headerEnabled" #list-header>
          <div class="pa-2 border-b">
            <v-text-field
              append-icon="$close"
              density="compact"
              prepend-inner-icon="mdi-magnify"
              hide-details
              @click:append="menu1 = false"
            />
          </div>
        </template>
        <template v-if="footerEnabled" #list-footer>
          <div class="d-flex justify-space-between pa-2 border-t">
            <v-btn prepend-icon="$prev" text="prev" variant="text" />
            <v-btn append-icon="$next" text="next" variant="text" />
          </div></template>
      </v-select>
      <v-btn text="btn after" />
    </v-container>
  </v-app>
</template>

<script setup>
  import { shallowRef } from 'vue'
  const menu1 = shallowRef(false)
  const footerEnabled = shallowRef(false)
  const headerEnabled = shallowRef(false)
  const forceNoData = shallowRef(false)
  const selectedItems = shallowRef([])
  const items = Array.from({ length: 215 }, (_, i) => ({ id: i, value: i * 10 }))
</script>

[J-Sek]

arrowDown will not act like tab when triggered in header/footer slots. This is exclusive feature of VList and a way to move focus from the input, but it brings more confusion when used elswhere

focus('last') in a virtualized list does not work (even without those changes) - try focusing VSelect without any slots and click ArrowUp to open the menu. When the list exceeds few hundreds, it lands at the last item rendered by virtual scroller. Better to push it as a future enhancement as it is just a minor inconvenience. Ideally, we would re-focus last focused item.