Add 'unsafeEncodeUtf' from os-string #231

Job	Run time
arm (arm32v7)	4m 10s
i386	4m 35s
arm (arm64v8)	3m 21s
darwin_arm (self-hosted, macOS, ARM64, 8.10.7)	11m 7s
build (ubuntu-latest, 8.6, 3.8.1.0)	5m 53s
darwin_arm (self-hosted, macOS, ARM64, 9.2.6)	27m 59s
build (ubuntu-latest, 8.8, 3.8.1.0)	5m 39s
darwin_arm (self-hosted, macOS, ARM64, 9.4.4)	10m 50s
build (ubuntu-latest, 8.10, 3.8.1.0)	5m 40s
build (ubuntu-latest, 9.0, 3.8.1.0)	5m 37s
build (ubuntu-latest, 9.2, 3.8.1.0)	3m 56s
build (ubuntu-latest, 9.4, 3.8.1.0)	4m 25s
build (ubuntu-latest, 9.6, 3.8.1.0)	3m 33s
build (ubuntu-latest, 9.8, 3.8.1.0)	3m 40s
build (macOS-latest, 9.4, 3.8.1.0)	28m 50s
build (macOS-latest, 9.6, 3.8.1.0)	9m 33s
build (windows-latest, 9.4, 3.8.1.0)	1m 21s
build (windows-latest, 9.6, 3.8.1.0)	3m 4s
	2h 23m 13s

Provide feedback