Feature: Keep the scroll position of the preview pane in sync with what's being edited

**- Do you want to request a *feature* or report a *bug*?**

*feature*

**- What is the current behavior?**

When you're authoring content, the preview pane either has to be scrolled separately or be in the "autoscroll" mode, which currently seems to mean "scroll the preview pane as many percent down as the content pane". When many individually collapsed and expanded editor components are involved, the autoscroll strategy most often scrolls to a place that's unrelated to what's being edited, so the manual scroll mode is the only usable option.

I'd share screenshots of my current setup, but I'm not at liberty to, unfortunately.

**- What is the expected behavior?**

That the preview pane automatically scrolls into view the preview of the content or component that's actually being edited.

I'm unsure about whether this is already possible without direct core support by using off-the-shelf react components and existing netlify-cms hooks. Pointers would be appreciated :)