fix(VDataIterator): emit page-count event

[nekosaur]

Description

we were not emitting the page-count event at all

Motivation and Context

closes #8886

How Has This Been Tested?

Markup:

<template>
  <div>
    <v-text-field label="search" v-model="search"></v-text-field>
    <v-data-iterator
      :items="desserts"
      :options.sync="options"
      :loading="loading"
      :items-per-page="pageSize"
      :page="page"
      @page-count="pageCountChanged"
      :search="search"
      hide-default-footer
    >
      <template v-slot:default="props">
        <v-row>
          <v-col cols="12" md="3" v-for="item in props.items" :key="item.name">
            <v-card role="button">
              <v-card-text class="text-center">
                <h4>{{ item.name }}</h4>
              </v-card-text>
            </v-card>
          </v-col>
        </v-row>
      </template>
    </v-data-iterator>
    <v-pagination v-model="page" :length="pageCount"></v-pagination>
  </div>
</template>

<script>
  export default {
    data () {
      return {
        search: '',
        totalDesserts: 0,
        pageCount: 0,
        page: 1,
        pageSize: 4,
        desserts: [
          {
            name: 'Frozen Yogurt',
            calories: 159,
            fat: 6.0,
            carbs: 24,
            protein: 4.0,
            iron: '1%',
          },
          {
            name: 'Ice cream sandwich',
            calories: 237,
            fat: 9.0,
            carbs: 37,
            protein: 4.3,
            iron: '1%',
          },
          {
            name: 'Eclair',
            calories: 262,
            fat: 16.0,
            carbs: 23,
            protein: 6.0,
            iron: '7%',
          },
          {
            name: 'Cupcake',
            calories: 305,
            fat: 3.7,
            carbs: 67,
            protein: 4.3,
            iron: '8%',
          },
          {
            name: 'Gingerbread',
            calories: 356,
            fat: 16.0,
            carbs: 49,
            protein: 3.9,
            iron: '16%',
          },
          {
            name: 'Jelly bean',
            calories: 375,
            fat: 0.0,
            carbs: 94,
            protein: 0.0,
            iron: '0%',
          },
          {
            name: 'Lollipop',
            calories: 392,
            fat: 0.2,
            carbs: 98,
            protein: 0,
            iron: '2%',
          },
          {
            name: 'Honeycomb',
            calories: 408,
            fat: 3.2,
            carbs: 87,
            protein: 6.5,
            iron: '45%',
          },
          {
            name: 'Donut',
            calories: 452,
            fat: 25.0,
            carbs: 51,
            protein: 4.9,
            iron: '22%',
          },
          {
            name: 'KitKat',
            calories: 518,
            fat: 26.0,
            carbs: 65,
            protein: 7,
            iron: '6%',
          },
        ],
        loading: true,
        options: {},
        headers: [
          {
            text: 'Dessert (100g serving)',
            align: 'left',
            sortable: false,
            value: 'name',
          },
          { text: 'Calories', value: 'calories' },
          { text: 'Fat (g)', value: 'fat' },
          { text: 'Carbs (g)', value: 'carbs' },
          { text: 'Protein (g)', value: 'protein' },
          { text: 'Iron (%)', value: 'iron' },
        ],
      }
    },
    methods: {
      pageCountChanged (v) {
        this.pageCount = v
      },
    },
  }
</script>

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Improvement/refactoring (non-breaking change that doesn't add any features but makes things better)

Checklist:

• The PR title is no longer than 64 characters.
• The PR is submitted to the correct branch (master for bug fixes and documentation updates, dev for new features and backwards compatible changes and next for non-backwards compatible changes).
• My code follows the code style of this project.
• I've added relevant changes to the documentation (applies to new features and breaking changes in core library)