Fix multi-level nesting issue with "v-for"

[noicu]

Something like this

  <template v-for="bar, i in bars" :key="i">
    <g-gantt-row :bars="bar.rows" highlight-on-hover />
    <template v-if="bar.child">
      <template v-for="col, j in bar.child" :key="`${i}${j}`">
        <g-gantt-row :bars="col.rows" highlight-on-hover />
      </template>
    </template>
  </template>