visionOS: update spatial pinch input to the current revision of godotengine/godot#123732

[Clancey]

What problem(s) does this PR solve?

• Moves the fork from the original revision of Add support for Spatial pinch input on visionOS godotengine/godot#123732 ("Add support for Spatial pinch input on visionOS" by Olivier Pinon, @oPinon), cherry-picked as fdd2c87, to the current revision. The upstream head used is 3d0e597f890cf4785310f4e95e202c5fc05a451a.

Additional information

Upstream design now carried

• Spatial events no longer register their own trackers. The system pinch (look and pinch) drives the shared left_hand / right_hand XRControllerTrackers through VisionOSSharedController, which VisionOSXRInterface owns. Accessories and hand gestures drive the same trackers. While a spatial event is active, it owns trigger_click and the default pose. The pose is corrected to the OpenXR hand interaction convention.
• The selection ray is published once per pinch as the default pose of a new /user/eyes_ext tracker.
• left_hand / right_hand are now always registered.

Conflicts and how existing fork behavior was preserved

fdd2c87 was applied after the gesture-derivation and scene-understanding commits, so the delta conflicts with fork code rather than the other way round. Resolution:

• Hand-derived gestures: VisionOSHandTracking no longer owns its own left_hand / right_hand trackers. publish_gestures writes into the shared controllers instead. While a spatial event is active, the optical pinch does not write trigger_click or the default pose. After the event ends, the optical trigger_click stays released until the optical pinch itself releases, so one pinch cannot click twice. Analog trigger, grip / grip_click, the aim / grip / palm poses and the visionos_hand_tracking profile still come from hand tracking. A hand with an accessory attached is still left to the accessory.
• Accessories: VisionOSControllerTracking uses the shared trackers. It skips a hand while a spatial event drives it. Haptics lookups are null-safe.
• Thread safety: the fork's engine-thread dispatch of spatial events and the [weak renderer] capture are kept. on_spatial_event is ignored until the interface is initialized.
• Lost head tracking: visionos_reset_input_tracking now resets the shared controllers. Its tests were updated.
• Scene understanding / face tracking / passthrough: these are unchanged.
• Fixes on top of upstream: eyes_ray.unref() (upstream calls unreference()), Hand::controller defaults to nullptr, null guards, and spatial-event state is reset on uninitialize. The shared trackers are created only after CompositorServices initialization succeeds, so a failed initialize does not leave them registered.

Downstream-visible changes

• Removed trackers: visionos/left_hand_pinch, visionos/right_hand_pinch, visionos/left_hand_ray, visionos/right_hand_ray.
  • LogicLand Ui/3d/xr_rig.gd (_spatial_pinch, _spatial_ray, _log_spatial_trackers) and tests/xr_rig_test.gd read these and must migrate before taking a release with this change. Otherwise gaze-and-pinch selection gets no ray.
  • Pinch: use left_hand / right_hand trigger_click, plus the default pose while pressed.
  • Ray: use the default pose of /user/eyes_ext. It is a single tracker shared by both hands and is updated once at the start of each pinch.
• A system pinch can no longer be told apart from an optical or accessory trigger by tracker name.
• During a system pinch, the default pose of left_hand / right_hand follows the spatial-event hand pose instead of the optical aim pose. Use aim for a stable optical aim.
• left_hand / right_hand exist even when hand and controller tracking are both disabled. Their descriptions changed to "visionOS left/right controller and spatial event".
• New VisionOSSharedController. VisionOSHandTracking::initialize lost its accessory flag, and VisionOSHandTracking::uninitialize was removed. VisionOSControllerTracking::initialize and VisionOSSpatialEventTracking::initialize take the shared controllers.

Validation

• scons platform=visionos target=template_release arch=arm64 dev_mode=yes module_text_server_fb_enabled=yes tests=no debug_symbols=no: passed
• Same flags with simulator=yes: passed
• scons platform=macos target=editor arch=arm64 dev_mode=yes module_text_server_fb_enabled=yes tests=yes: passed
• godot.macos.editor.arm64 --headless --test --test-case="*visionOS*": 56 test cases and 11390 assertions passed. This includes the new spatial-event arbitration test and the updated lost-head-tracking test.
• godot.macos.editor.arm64 --headless --test --test-case="*XR*,*[XR]*": passed
• xmllint on VisionOSXRInterface.xml: passed
• Not run: on-device testing on Apple Vision Pro.

Coordination

• The unmerged clancey-qr-tracking-native-contract branch changes visionos_xr_interface.{h,mm} and scene understanding. It will likely need a rebase and conflict resolution against this change, mainly in VisionOSXRInterface::initialize / uninitialize.
• Merging into visionos-4.8 republishes the visionos-latest release that LogicLand CI consumes. Hold the merge until LogicLand has migrated off the removed tracker names.