Add load listener to live preview component

[KevinBatdorf]

Description

This PR attempts to solve height issues that appear within live preview pattern components. It adds an event listener to the nested iFrame that will listen for load events that bubble up, and fire a resize event to trigger a re-render (if the height/width have changed). There is also a 100ms debounce wrapper.

I couldn't find a comprehensive list of what fires the load event, but images are probably the main concern here. I know stylesheets (link tags) and other items also fire the event.

Testing Instructions

I'm not confident in how to reproduce this as it seems to only happen to me on occasion. It happens enough though that I do have screenshots and video of it though. It's also happening to others on our team as well, so I suspect its common.

(maybe others can chime in if they've experienced this as well)

Screenshots

Example of it being cut off:

Component renders that occur before this PR + load events logged (onLoad={console.log}):

This PR, showing the additional render after incoming load events

Types of changes

Enhancement

Checklist:

• My code is tested.
• My code follows the WordPress code style.
• My code follows the accessibility standards.
• I've tested my changes with keyboard and screen readers.
• My code has proper inline documentation.
• I've included developer documentation if appropriate.
• I've updated all React Native files affected by any refactorings/renamings in this PR (please manually search all *.native.js files for terms that need renaming or removal).
• I've updated related schemas if appropriate.

[jorgefilipecosta]

cc: @youknowriad that I think was looking into improving the pattern previews.