Doc: Fix missing lights images

Add missing 3D lights icons.

Task-number: QDS-8433
Change-Id: Iaebe003efcaecbaf394dc4383f4de722d30142fe
Reviewed-by: Leena Miettinen <riitta-leena.miettinen@qt.io>

doc/qtdesignstudio/src/qtquick3d-editor/qtdesignstudio-3d-lights.qdoc

@@ -41,25 +41,25 @@
         \li More Information
 
     \row
-        \li \inlineimage directional.png
+        \li \inlineimage icons/directional.png
         \li Directional Light
         \li
         \li \l{DirectionalLight}{Light Directional}
 
     \row
-        \li \inlineimage point.png
+        \li \inlineimage icons/point.png
         \li Point Light
         \li
         \li \l{PointLight}{Light Point}
 
     \row
-        \li \inlineimage spot.png
+        \li \inlineimage icons/spot.png
         \li Spot Light
         \li
         \li \l{SpotLight}{Light Spot}
 
     \row
-        \li \inlineimage area.png
+        \li \inlineimage icons/area.png
         \li Area Light
         \li \inlineimage ok.png
         \li \l{AreaLight}{Light Area}