xrt: Support EXT_eye_gaze_interaction extension
Add support for EXT_eye_gaze_interaction, including:
- Support
XrSystemEyeGazeInteractionPropertiesEXT
forxrGetSystemProperties
call. - New user path:
/user/eyes_ext
. - New input source:
…/input/gaze_ext/pose
. - Support
XrEyeGazeSampleTimeEXT
forxrLocateSpace
call.