feat(date-picker): add singlePanel API

[jmni-cn]

<template>
  <n-date-picker
    v-model:value="range"
    type="daterange"
    single-panel
    clearable
  />
  <n-date-picker
    v-model:value="range"
    type="daterange"
    panel
    single-panel
    clearable
  />
  <pre>{{ JSON.stringify(range) }}</pre>
</template>

<script setup lang="ts">
import { ref } from 'vue'

const range = ref<[number, number]>([Date.now(), Date.now()])
</script>

&

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