cmake: add include directory usage requirements

CMakeLists.txt

@@ -205,6 +205,11 @@ vtk_module_add_module(vtkqttesting
   HEADERS ${QtTesting_DEVEL_HEADERS}
   HEADERS_SUBDIR "vtkqttesting"
 )
+target_include_directories(vtkqttesting
+  PUBLIC
+    "$<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}>"
+    "$<BUILD_INTERFACE:${CMAKE_CURRENT_BINARY_DIR}>"
+    "$<INSTALL_INTERFACE:${_vtk_build_HEADERS_DESTINATION}/vtkqttesting>")
 
 if (FALSE) # XXX(kitware): ParaView does this already.
 # Set library name to include custom prefixes/suffixes.