Live-Preview: Improve window rendering with larger specified breakpoints.

[PatrikKozak]

Suggestion by @ericuldall in #4576

Larger breakpoints tend to render off screen if larger than the available width of the window.

A few options to improving the behavior of this would be:

• Make the screen proportional based on the breakpoint size and width available, similar to how chrome does this in their mobile/table screen view (preferred approach. Something like this:
  
• Add in overflow scroll

[ericuldall]

The other problem is if I scale down to 50%, why does the image move all the way to the right side of the preview area? I think there's some other bugs here.

[ericuldall]

I do generally like the idea of thinking in terms of aspect ratio rather than exact size. It's a preview and I think fitting the correct aspect ratio as large as possible in the preview area is ideal.

[tijsomnicasa]

The old plugin for previews (pemedia/payload-visual-editor) used to handle this with transforming the div