Adding USD runtime export for Android and iOS

[andybak]

Ticket #178 was closed - either erroneously or at the very least without any explanation.

I'm sure I'm not the only person holding off on USD until I know if it's feasible outside of desktop-only environments. Please can #178 either be reopened or at least updated with a clear reason for why the ticket was closed and whether Unity ever plans to support USD on Android or iOS?

[lruminski]

Bump.

Would like to know the status of this as well.