feat: update grid system to Vue 3

[KaelWD]

No major changes - just composition API, prefixed classes, and removed the old grid system.

BREAKING CHANGE: grid classes now have a v- prefix
BREAKING CHANGE: v-layout, v-flex, and <v-container grid-list-{size}> have been removed

Markup:

<template>
  <v-app>
    <v-container class="grey lighten-5">
      <div class="display-1">New grid</div>
      <p>Margins y around red elements are larger</p>
      <v-row dense>
        <v-col
          :cols="12"
          class="green"
        >col 1</v-col>
        <v-col :cols="12">
          <v-row dense>
            <v-col class="red">col 2</v-col>
            <v-col class="red">col 3</v-col>
            <v-col class="red">col 4</v-col>
          </v-row>
        </v-col>
        <v-col class="green">col 5</v-col>
        <v-col class="green">col 6</v-col>
        <v-col
          cols="12"
          class="green"
        >col 7</v-col>
      </v-row>
    </v-container>

    <v-container class="grey lighten-5">
      <div class="display-1">New grid with gutters</div>
      <p>Margins y around red elements are larger</p>
      <v-row dense>
        <v-col :cols="12">
          <v-card
            class="pa-2 green"
            outlined
          >
            col 1
          </v-card>
        </v-col>
        <v-col :cols="12">
          <v-row dense>
            <v-col>
              <v-card
                class="pa-2 red"
                outlined
              >
                col 2
              </v-card>
            </v-col>
            <v-col>
              <v-card
                class="pa-2 red"
                outlined
              >
                col 3
              </v-card>
            </v-col>
            <v-col>
              <v-card
                class="pa-2 red"
                outlined
              >
                col 4
              </v-card>
            </v-col>
          </v-row>
        </v-col>
        <v-col>
          <v-card
            class="pa-2 green"
            outlined
          >
            col 5
          </v-card>
        </v-col>
        <v-col>
          <v-card
            class="pa-2 green"
            outlined
          >
            col 6
          </v-card>
        </v-col>
        <v-col cols="12">
          <v-card
            class="pa-2 green"
            outlined
          >
            col 7
          </v-card>
        </v-col>
      </v-row>
    </v-container>
  </v-app>
</template>

<script>
  import { h } from 'vue'

  export default {
    components: {
      VCard: (props, { slots }) => h('div', slots.default?.()),
    },
  }
</script>