tests: add test cases for wide character path conversions #562

Job	Run time
windows (msvc-14.2, 14,17, 32,64, windows-2019)	33m 45s
posix (gcc-6, 14,1z, ubuntu-latest, ubuntu:18.04, g++-6)	13m 47s
windows (gcc, 14,17, 64, windows-2019)	1m 32s
posix (gcc-7, 14,17, g++-7, ubuntu-20.04)	13m 13s
windows (msvc-14.3, 14,17, 32,64, windows-2022)	36m 4s
posix (gcc-8, 14, ubuntu-20.04, g++-8)	6m 54s
posix (gcc-9, 14,17, ubuntu-20.04, g++-9)	16m 3s
posix (gcc-10, 14,17, ubuntu-20.04, g++-10)	13m 21s
posix (clang, clang++-3.9, 14, ubuntu-latest, ubuntu:18.04, clang-3.9)	8m 32s
posix (clang, clang++-4.0, 14, ubuntu-latest, ubuntu:18.04, clang-4.0)	7m 41s
posix (clang, clang++-5.0, 14,1z, ubuntu-latest, ubuntu:18.04, clang-5.0)	13m 31s
posix (clang, clang++-6.0, 14,17, ubuntu-20.04, clang-6.0)	14m 26s
posix (clang, clang++-7, 14,17, ubuntu-20.04, clang-7)	13m 47s
posix (clang, clang++-8, 14,17, ubuntu-20.04, clang-8)	14m 34s
posix (clang, clang++-9, 14,17, ubuntu-20.04, clang-9)	14m 32s
posix (clang, clang++-10, 14,17, ubuntu-20.04)	14m 55s
posix (clang, 14,17, macos-12)	13m 53s
	4h 10m 30s

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