1. Adds a `libdevilution_so` target when tests are enabled.
2. Each test file is now a separate binary target linked against `libdevilutionx_so` (can now run tests in parallel).
3. Tests are now defined in a separate `test/CMakeLists.txt` file.
4. Building the tests is now controlled by the standard `BUILD_TESTING` option (defined by CTest).
5. Tests are now built by default.
6. On CI, test errors are now reported.
Also:
* `.clang-format`: Enable SortIncludes in tests
* `path_test.cpp`: Fix -Wsign-compare
This is mainly to help me test code builds under GCC faster than pushing to the remote and letting the build server do it. If someone without WSL installed selects the build target they'll get an error in their IDE, but no harmful impact other than that. The variables should be populated for any WSL2 installation. No idea about WSL1.
The whitespace in this file is showing significant changes because visual studio regenerates the whole file when a change is made, I didn't think it was worth reverting since it'll happen again next time someone makes a change (seems it defaults to spaces...). Added an entry to .editorconfig documenting the format used.