How about "expose GridLayout.layoutUpdate" ?

## How about "expose GridLayout.layoutUpdate" ?

Sometimes, when a layout data is changed, but the UI interface is not synchronized, I try to expose 'GridLayout.layoutUpdate()' and find it very effective.

```vue
// node_modules\vue-grid-layout-v3\src\components\GridLayout.vue
...
defineExpose({
  emitter,
  placeholderRef,
  layoutUpdate
});
...
```
