feat(VDatePicker): add scrollable month navigation

[ascott18]

Adds wheel and swipe month navigation behind the scrollable prop in VDatePickerMonth.

Updates docs and API prop copy with a new scrollable example for v-date-picker.

Description

Restores opt-in scrollable behavior that VDatePicker had in Vuetify 2, allowing for natural interactions on both desktop and mobile.

Fixes #22928
Fixes #19176

Markup:

<template>
  <v-app>
    <v-container class="py-8">
      <v-row>
        <v-col cols="12" md="6">
          <div class="text-subtitle-1 mb-2">scrollable = true</div>
          <v-date-picker
            v-model="dateA"
            scrollable
            show-adjacent-months
          />
        </v-col>

        <v-col cols="12" md="6">
          <div class="text-subtitle-1 mb-2">scrollable = false</div>
          <v-date-picker
            v-model="dateB"
            show-adjacent-months
          />
        </v-col>
      </v-row>
    </v-container>
  </v-app>
</template>

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

  const dateA = ref('2026-01-15')
  const dateB = ref('2026-01-15')
</script>

[J-Sek]

Renamed scrollable to wheel as it is going to mirror same prop from VWindow. MD3 actually defines a scrollable/continuous variant of the picker that we may land in v4.4 or v4.5, so that prop name would be expected for that variant.

v2 accepted vertical scroll and swipe, but I don't think it is practical. It hijacks normal scroll and got me surprised/frustrated immediately. We will ship only horizontal scroll.