feat(VSlider): add start and end events

[nekosaur]

Description

closes #15675

Markup:

<template>
  <div class="ma-10" @mouseup="foo">
    <v-slider
      :model-value="model"
      @end="end"
    ></v-slider>
    <pre>{{ model }}</pre>
    <v-range-slider
      :model-value="model2"
      @end="end2"
    ></v-range-slider>
    <pre>{{ model2 }}</pre>
  </div>
</template>

<script>
  export default {
    data: () => ({
      model: 10,
      model2: [10, 20],
    }),
    methods: {
      end (v) {
        this.model = v
      },
      end2 (v) {
        this.model2 = v
      },
    },
  }
</script>