st/oxr: Provide handle lifecycle management

src/xrt/state_trackers/CMakeLists.txt

src/xrt/state_trackers/oxr/oxr_api_instance.c

src/xrt/state_trackers/oxr/oxr_api_session.c

src/xrt/state_trackers/oxr/oxr_api_space.c

src/xrt/state_trackers/oxr/oxr_api_swapchain.c

src/xrt/state_trackers/oxr/oxr_api_verify.h

src/xrt/state_trackers/oxr/oxr_handle.h

src/xrt/state_trackers/oxr/oxr_handle_base.c

src/xrt/state_trackers/oxr/oxr_instance.c

src/xrt/state_trackers/oxr/oxr_objects.h

src/xrt/state_trackers/oxr/oxr_session.c

src/xrt/state_trackers/oxr/oxr_session_gl.c

src/xrt/state_trackers/oxr/oxr_session_vk.c

src/xrt/state_trackers/oxr/oxr_space.c

src/xrt/state_trackers/oxr/oxr_swapchain.c