tests: Enable unit test on Windows

Allow run some unit tests on Windows.
* Remove hardcoded path separator in whitelist env for Meson to choose
  OS-specific separator automatically (i.e., ';' for windows and ':' for *nix)
* Add dependency explicitly for some test cases, otherwise plugins couldn't be
  loaded on uninstalled environment of Windows.
6 jobs for windows-unittest in 33 minutes and 5 seconds (queued for 14 minutes and 58 seconds)