[Feature Request] Slot for group in VTreeview

[jelle-eastground]

Problem to solve

In VTreeview there seems no way to customize a group using the slots, because only a slot for an item is available.

Proposed solution

It would be great if a group slot with props is exposed in VTreeview, to be able to do the following:

<template>
  <v-treeview>
    <!-- missing: -->
    <template v-slot:group="{ props }">
      <v-treeview-group v-bind="props"/>
    </template>

    <!-- already available: -->
    <template v-slot:item="{ props }">
      <v-treeview-item v-bind="props"/>
    </template>
  </v-treeview>
</template>

Could this group slot be added? I think this issue is related.