move Filament headers to own directory under iOS/macOS

macos/include/viewer/ViewerGui.h

@@ -231,6 +231,8 @@ public:
 
     int getCurrentCamera() const { return mCurrentCamera; }
 
+    float getOcularDistance() const { return mOcularDistance; }
+
 private:
     using SceneMask = gltfio::NodeManager::SceneMask;
 
@@ -266,6 +268,9 @@ private:
     SceneMask mVisibleScenes;
     bool mShowingRestPose = false;
 
+    // Stereoscopic debugging
+    float mOcularDistance = 0.0f;
+
     // 0 is the default "free camera". Additional cameras come from the gltf file (1-based index).
     int mCurrentCamera = 0;