build: rename build-related dirs

Problem:
Dirs "config", "packaging", and "third-party" are all closely related
but this is not obvious from the layout. This adds friction for new
contributors.

Solution:
- rename config/ to cmake.config/
- rename test/config/ to test/cmakeconfig/ because it is used in Lua
  tests: require('test.cmakeconfig.paths').
- rename packaging/ to cmake.packaging/
- rename third-party/ to cmake.deps/ (parallel with .deps/)

cmake.deps/cmake/RemoveFiles.cmake

@@ -0,0 +1,5 @@
+file(GLOB_RECURSE FILES_TO_REMOVE ${REMOVE_FILE_GLOB})
+
+if(FILES_TO_REMOVE)
+  file(REMOVE ${FILES_TO_REMOVE})
+endif()