Function updateXrTeleportation

Drive teleportation for the current frame: read each controller's thumbstick, aim a parabolic arc + floor reticle while it's pushed forward, teleport (and rotate to the chosen heading) on release, and snap-turn on sideways pushes. Returns the (possibly new) reference space — the caller must adopt it for subsequent frames (the teleportation feature does this automatically). Call once per XR frame after updateXrInputPoses.