[Hoverable] Add support for an external controller

[titouanmathis]

As of now, the Hoverable component only provides support for moving a target inside a parent element.

<div data-component="Hoverable"> <!-- ← parent -->
  <div data-ref="target">...</div> <!-- ← target -->
</div>

We might need to have the same behavior, but based on the pointer movements on another element.

<div data-component="HoverableController"></div> <!-- ← controller -->

<div data-component="Hoverable"> <!-- ← parent -->
  <div data-ref="target">...</div> <!-- ← target -->
</div>

Example implementation: playground