feat(VSlider): introduce track disabled

[mrooding]

Description

resolves #20872

The current implementation keeps the overall structure and event listeners in place. It simply ignores click events if they do not come from the thumb element.

I'm happy to discuss alternative options but would like to get some feedback first.

Markup:

<template>
  <v-app>
    <v-container>
      <v-slider :track-disabled="true" @end="onChange" />
    </v-container>
  </v-app>
</template>

<script>
  export default {
    name: 'Playground',
    setup () {
      return {
        //
      }
    },
    methods: {
      onChange (value) {
        console.log(value)
      }
    }
  }
</script>

[mrooding]

Another solution could be to modify when we add pointer-events: none; using a css class. If we remove that from the overall container but keep it on the thumb it should also suffice. We could then remove the guard check inside the click event.