Implement lancelot testing using the XCode emulator (visionOS)

The simulator for visionOS is less featureful then what we have available for the OpenXR through the meta xr simulator (i.e., There's no emulation of anchors, pass-through or multiview ). In addition the approach will be slightly different visionOS applications are running completely inside the emulator as a visionOS application. The upside is that we should be able to just query the emulator for a screen capture so no scene grabber needed.