scrollable-region-focusable should consider an element's content real content, not its content box

[WilcoFiers]

The following shouldn't fail the scrollable-region-focusable rule:

<style>
  #container {
    width: 300px;
    background: #aff;
    overflow-y: auto;
  }
  p {
    width: 600px;
  }
</style>
<div id="container">
  <p>Contents</p>
</div>

The text in this paragraph is fully visible. Axe-core is failing this because its detecting a p element who's content box ix much larger than it scrollable parent. Axe shouldn't use the content box here though, it should use the actual size and position of the element's content.