fix(main-scroll): obtain observed container element reliably to work with any Vue version

[joseacabaneros]

Obtain observed container element reliably to work with any Vue version

With the following code, we are able to retrieve the root element of a renderless component in both Vue 2 and Vue 3:

onMounted(() => {
   containerRef.value = getCurrentInstance()?.proxy?.$el;
});
...
return () => slots.default?.()[0];

In Vue 2 and Vue 3:

• slots.default?.() -> Gives an array of vNodes | [0] Gets the vNode root and renders it

IF we would return the full array of vNodes return () => slots.default?.():

• In Vue 2: Renders the vNodes as it is without problem, and we can get the root element with getCurrentInstance()?.proxy?.$el. Only if the default slot has a single node, otherwise, Vue will throw an error
  [Vue warn]: Multiple root nodes returned from render function. Render function should return a single root node.
• In Vue 3: Renders the vNodes as a Fragment (because in Vue3 supports multiple root nodes) and when we do getCurrentInstance()?.proxy?.$el it gives a #text node because the root node is the Fragment.

One more thing, this scope will support attrs inheritance in both Vue versions ✌🏾