feat(VDatePicker): keyboard arrows navigation in selection grid

[J-Sek]

resolves #5629

Markup:

Screencast.from.2026-05-12.18-43-11.mp4

Markup:

<template>
  <v-app>
    <v-container>
      <v-row class="mb-4">
        <v-col cols="auto">
          <v-switch v-model="color" :false-value="undefined" label="color=primary" true-value="primary" hide-details />
        </v-col>
        <v-col cols="auto">
          <v-switch v-model="showAdjacentMonths" label="adjacent months" hide-details />
        </v-col>
        <v-col cols="auto">
          <v-switch v-model="customWeekdays" :false-value="undefined" :true-value="[1,2,3,4,5]" label="weekdays=[1,2,3,4,5]" hide-details />
        </v-col>
      </v-row>

      Multiple:
      <v-chip-group v-model="multipleIndex" mandatory>
        <v-chip :value="0">false</v-chip>
        <v-chip :value="1">true</v-chip>
        <v-chip :value="2">range</v-chip>
      </v-chip-group>

      <v-date-picker
        v-model="msg"
        :color="color === 'undefined' ? undefined : color"
        :multiple="multipleOptions[multipleIndex]"
        :show-adjacent-months="showAdjacentMonths"
        :weekdays="customWeekdays"
      />
      <pre>{{ JSON.stringify(msg, null, 2) }}</pre>

      <input type="date">
    </v-container>
  </v-app>
</template>

<script setup>
  import { ref } from 'vue'

  const msg = ref()
  const color = ref('primary')
  const showAdjacentMonths = ref(false)
  const customWeekdays = ref(undefined)
  const multipleOptions = [false, true, 'range']
  const multipleIndex = ref(0)
</script>