Intern MakeFileResolver defines and include paths.
This decreases the memory consumption for the defines/include paths as queried by the CMake JSON import job considerably. And, since we can now reuse existing Path instances, we don't need the costly conversion most of the time, leading to a considerable performance win as well. Before, my kdevelop session took ca. ~230MB of memory, now this number is down to ~153MB. Performance wise, I saw the kdevplatform JSON file speed up from ~2.2s evaluation down to ~1.4s.