feat: added immersive window support for VR race views

- Introduced a new configuration option for immersive window mode in runtime_config.h.
- Updated the parsing and setting functions to handle the immersive window state.
- Modified the OpenXR backend to support rendering with the immersive window, blending the race view with the surrounding environment.
- Enhanced the settings overlay to allow users to select between immersive, immersive window, and flat screen race views.
- Implemented GPU rendering logic for the immersive window mask, ensuring correct visual output in various rendering paths.
- Added tests to validate the immersive window functionality and its interaction with existing race view settings.

aurora-main/lib/aurora.cpp

@@ -815,6 +815,7 @@ gfx::StereoReplayFrame make_stereo_replay_frame(const AuroraStereoFrame& input,
   std::memcpy(&anchorFromScene, sceneAnchor.anchorFromScene.data(), sizeof(anchorFromScene));
   gfx::StereoReplayFrame replay{};
   replay.cockpit = input.cockpit;
+  replay.window = input.mode == AURORA_STEREO_FRAME_IMMERSIVE_REPLAY && input.window;
   // The sealed guest frame owns its scale. The packet may have been sampled
   // just before a change of scale (a character swap, a lightning strike), so
   // only its head/IPD translation is rescaled to the frame's.
@@ -2216,6 +2217,10 @@ std::vector<PresentationJob> encode_sealed_frame(gfx::SealedFrame& sealedFrame,
       encode_virtual_screen_eye(encoder, completedMono, eye);
       const auto& output = g_stereoEyeTargets[eye].output();
       stereo_overlay::composite_flat(encoder, output.view, output.size, eye);
+      // An immersive packet that could not be replayed still goes out as a windowed layer.
+      if (ctx.stereoReplay->window) {
+        gfx::mask_stereo_eye_output(sealedFrame, encoder, *ctx.stereoReplay, eye, output.view, output.size);
+      }
     }
     if (mirrorPlan == MirrorPlan::Black && !headsetOnly) {
       encode_presentation_snapshot(encoder, ctx.presentSource, *finalImage, true, MirrorPlan::Black,