Allow different hotkeys to be bound to different Render display choices

Currently (as of a recent patch in 2.81) we can set in the preferences if we want our render to display in the Image viewer, a new window, full screen, or keep UI as is. I mostly like this change, as for most of projects it always stays set on the "Keep UI," option.

However, when I'm messing around and don't want to mess around with the UI a bunch, it would be nice to be able to hit something like "Alt + F12" to render in a new window or something, instead of having to change it in preferences just for one project. Being able to bind your own hotkeys to these options would be great.