RFC: Make stage space pose space for select drivers
There is currently a problem in the space overseer that causes locating LOCAL in STAGE or STAGE in LOCAL to not have the position tracked flags set.
The root cause is that local was an offset space and stage space was a reference to the root space. Not setting position tracked flags when locating one in the other isn't logically wrong here because nothing here is actually tracked by any tracking system.
As a general improvement this lets xrt_devices (currently limited to HMDs) announce that they can track stage spaces and return poses for XRT_INPUT_GENERIC_STAGE_SPACE_POSE
s. For lighthouse tracked devices this is always implicitly (0, 0, 0) because right now we imagine the poses we return to always be relative to that imagined stage space, thought his might change depending on how we implement room setup / calibration.
LOCAL in STAGE or STAGE in LOCAL should probably be position tracked for the devices that don't have stage_supported too, but that's TBD.