Linux: Investigate the user document path when executing as root

[i8degrees]

I would like to know what the returned document directory path here is when executing tests as root. (This is from a Docker container build).

xvfb-run tests/Debug/ActionTest

ERROR: [ UnitTest.cpp : 246 ] Could not determine the user's documents directory path.
ERROR: [ UnitTest.cpp : 247 ] Please fix this issue before running these tests.

(Nevermind the reality that I would never care to support running any engine test with root privileges, nor does the engine have any reason for superuser privileges).

[i8degrees]

The reason for this issue is because the UnixFile class implementation we use is incomplete. The paths given inside the file -- src/system/UnixFile.cpp are mostly static strings.

Preliminary work on resolving this issue is already under way, using the POSIX APIs that are available on Darwin and Linux, such as the getenv syscall.

[i8degrees]

I have since discovered another detail that needs cleanup before v1.0.0.

• nomlib-system - this is the library target that contains the compilation files for UnixFile, WinFile, etc. i.e.: src/system/ and include/nomlib/system.

• nomlib-file - existing library target where the file impl and headers need to be relocated to. See src/file/CMakeLists.txt

I have begun cleanup of this subsystem in addition to the implementation of a new File I/O class for Darwin derived platforms.

See git branch feature/split-unix-darwin-file-impl