New 'visible' event emitted when the scroller becomes visible

Author: Guillaume Chau

src/components/VirtualScroller.vue

@@ -365,6 +365,7 @@ export default {
 
     handleVisibilityChange (isVisible, entry) {
       if (this._ready && (isVisible || entry.boundingClientRect.width !== 0 || entry.boundingClientRect.height !== 0)) {
+        this.$emit('visible')
         this.$nextTick(() => {
           this.updateVisibleItems()
         })