message: [Improvement] Tabbar: optimize DOM
diff: <div :class="b({ active })" @click="onClick">
  <div :class="b('icon', { dot })">
  <slot name="icon" :active="active">
  - <icon v-if="icon" :name="icon" />
  + <icon v-if="icon" :name="icon" :info="info" />
  </slot>
  - <div v-if="isDef(info)" class="van-icon__info">{{ info }}</div>
  </div>
  <div :class="b('text')">
  <slot :active="active"/>
  