Selection updates from Web APIs should scroll to reveal selection in scrollable containers

[shwetabin]

Current spec doesn't define whether setting selection through Web APIs should scroll to reveal the selection.

Case: Caret in scrollable container

<div style="width: 200px; height: 50px; overflow: auto;">
  <p>Line 1</p>
  <p>Line 2</p>
  <p id="target">Line 3 - below fold</p>
</div>

selection.collapse(target.firstChild, 5);

Browser behaviors:
Chromium - No scroll, caret not visible
Safari - No scroll, caret not visible
Firefox - Scrolls to reveal caret ✓

Proposed Behaviour

Selection should scroll the closest scrollable ancestor to reveal the selection.