Retrieves the camera's mask id.
This id is used to mark whether the camera should be used / drawn to in sync and object masks.
The id cannot be manually set; if a camera is deleted and another one created, the new camera will get the id of the deleted one.
When automatically rendered from the DX11 SYNC function, the camera's will be rendered in reverse order so that the one with the
highest ID gets rendered first and the lowest id (which is always the main camera) last.
You can however set the automatic sync mask to 0 and draw the cameras in whatever order you see fit, with multiple passes if desired, using
the RENDER CAMERA function.
