I had decided against using "both" for the resize as it allows the iframe to flow outside its horizontal boundary and severely overlap with potential elements rendered side-by-side e.g:
I don't think we should enable this by default.

The keyboard shortcuts for toggling full screen are ctrl+shift+f and setting Esc as a shortcut has even more unintended consequences.

Another option is to use the fullscreen_native setting, which will use the browser native API for full screen and supports the Esc key. In fact I think I prefer this approach now that I've tried it. Here is an alternative PR: #4045