Add option to render a regular camera view on the non-LG display

[hybridherbst]

Right now, the three options (swizzle, center, quilt) all show a distorted / stretched view of the content.

Would be great if, similar to https://immersive-web.github.io/webxr-samples/spectator-mode.html, the original screen could still be rendered properly and stay interactive. For example, for presentations it's very much desired to control from that first monitor and have a "clean" presentation on LG, without messing with the cursor in the LG window.

Distorted "center" view visible on the right side, because it's just a blit copy of the left side - should be a proper separate rendering: