Consider inline scene drawing

[adepke]

The current method of getting the scene output in the editor GUI is to use a separate fullscreen render target, which acts as a back buffer texture. This is very wasteful with respect to GPU memory bandwidth, so consider drawing the scene inline with the editor GUI using ImDrawCallbacks.

[adepke]

Decided the current rendering separation is much better than what would be required to implement this feature, also the performance impact is not of significant concern.