add ability to switch code position and chart position

I'm left-handed, so I happen to prefer to see code on the left and the window that renders the code on the right. It would be cool of blockbuilder allowed the user to switch the horizontal position of the code and the chart (rendering window)

No file or test is named in the issue. Start by locating the browser UI entry point that lays out the code and chart, then verify the arrangement can be switched horizontally and that both positions render correctly.

Written by the indexing model from the issue text.