Add support for using components as icons

[jamesWalker55]

This allows using any arbitrary icon as the argument to 'icon', as long as the icon is a component.

Related issue: #12

Example usage with antfu/unplugin-icons:

<script lang="ts" setup>
import VueFileToolbarMenu from 'vue-file-toolbar-menu';
import Icon from '~icons/ph/tag';

import {computed} from 'vue';

const my_menu = computed(() => [
      {
        text: 'My Menu', menu: [
          {text: 'Item 1', click: () => alert('Action 1')},
          {text: 'Item 2', icon: 'sentiment_very_satisfied'},
          {text: 'Item 3', icon: Icon},
        ],
      },
      {
        icon: Icon,
        click: () => alert("Icon button!"),
      },
    ],
);
</script>

<template>
  <VueFileToolbarMenu :content="my_menu"/>
</template>

[motla]

Hi @jamesWalker55
Thank you very much for your contribution!! 🙂
I just released v1.5.0 (Vue2) and v2.2.0 (Vue3) including your commits.