Centre foveation on the player's gaze on headsets with eye tracking

With [vr] eye_tracked_foveation (on by default on the Steam Frame, off
elsewhere) the runtime asks for XR_EXT_eye_gaze_interaction. When the
system reports an eye tracker, OpenXRInput binds the gaze pose and
locates it for each packet's display time, in the space the eye views
are located in; vr/eye_gaze.h turns it into tangents of each eye's own
view, which AuroraStereoFrame now carries (appended, after the existing
prefix).

Aurora centres the eye's fragment density map on the gaze snapped to a
cell of two map texels (about 3 degrees). Each eye keeps up to 32 maps,
one per cell looked at, so a glance back reuses its map; a new map is
bound once its upload completes, and until then the eye keeps the map
it had. Without a tracked gaze (a blink, no tracker, the setting off)
foveation centres on the forward direction exactly as before: the
forward maps are byte-identical.

Also logs every extension the OpenXR runtime offers at startup, so the
first Steam Frame session shows what SteamVR's Android runtime has.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_019HBRGKTE1GnN2ah8gcZKr3

runtime/CMakeLists.txt

@@ -456,6 +456,11 @@ add_executable(mkw_vr_wii_remote_tests "${CMAKE_CURRENT_LIST_DIR}/tests/vr_wii_r
 target_include_directories(mkw_vr_wii_remote_tests PRIVATE "${CMAKE_CURRENT_LIST_DIR}/include")
 target_compile_features(mkw_vr_wii_remote_tests PRIVATE cxx_std_17)
 add_test(NAME mkw_vr_wii_remote_tests COMMAND mkw_vr_wii_remote_tests)
+# Eye-tracked foveation: the gaze in each eye's view (vr/eye_gaze.h).
+add_executable(mkw_vr_eye_gaze_tests "${CMAKE_CURRENT_LIST_DIR}/tests/vr_eye_gaze_tests.cpp")
+target_include_directories(mkw_vr_eye_gaze_tests PRIVATE "${CMAKE_CURRENT_LIST_DIR}/include")
+target_compile_features(mkw_vr_eye_gaze_tests PRIVATE cxx_std_17)
+add_test(NAME mkw_vr_eye_gaze_tests COMMAND mkw_vr_eye_gaze_tests)
 
 # The in-headset settings panel's controller chord, release latch, selection,
 # scrolling and canvas mapping, plus the thread bridge they publish through.