Constrain MRE within a limited physical area

[sorenhan]

This one is hard, but has been requested a couple of times - would it be possible to set a region and constrain all MRE content (geometry, props etc) within it. Conversely, would it be possible to calculate the boundary of the current MRE.

This is a hard problem for a number of reasons- for example, MRE doesn't know about GLTF regions (it would know the transforms, but not the size of the prop), it doesn't limit attachments to stay within a region, and it is impossible to know how large a "CreateFromLibrary" actor is.