This fixes our use of std::filesystem to interpret all paths names as
UTF8. Before this, UTF8 paths did not work correctly in all cases.
This also adds a new unit test to cover this case.
On Windows, it is critical that a UTF8 locale be set at runtime.
Applications linking with Packager as a library should call setlocale(),
and the Packager frontends now do this automatically after converting
wide character arguments into narrow strings.
Closes#652
5a2571b9bc