extract the world<->widget transform into WorldCoordinates

src/test/CMakeLists.txt

@@ -12,6 +12,7 @@ add_files(
     SurfaceMaskTest.cpp
     BeltDragPathTest.cpp
     TunnelCompletionTest.cpp
+    WorldCoordinatesTest.cpp
     BuildingTest.cpp
     BuildingConfigTest.cpp
     ShipTest.cpp