Add 'unsafeEncodeUtf' from os-string #235

Job	Run time
darwin_arm (self-hosted, macOS, ARM64, 8.10.7)	1s
darwin_arm (self-hosted, macOS, ARM64, 9.2.6)	1s
darwin_arm (self-hosted, macOS, ARM64, 9.4.4)	1s
i386	4m 39s
arm (arm32v7)	4m 4s
build (ubuntu-latest, 8.6, 3.8.1.0)	5m 44s
arm (arm64v8)	3m 5s
build (ubuntu-latest, 8.8, 3.8.1.0)	5m 25s
build (ubuntu-latest, 8.10, 3.8.1.0)	5m 18s
build (ubuntu-latest, 9.0, 3.8.1.0)	5m 20s
build (ubuntu-latest, 9.2, 3.8.1.0)	4m 0s
build (ubuntu-latest, 9.4, 3.8.1.0)	4m 29s
build (ubuntu-latest, 9.6, 3.8.1.0)	3m 12s
build (ubuntu-latest, 9.8, 3.8.1.0)	3m 9s
build (macOS-latest, 9.4, 3.8.1.0)	9m 34s
build (macOS-latest, 9.6, 3.8.1.0)	26m 44s
build (windows-latest, 9.4, 3.8.1.0)	17m 51s
build (windows-latest, 9.6, 3.8.1.0)	17m 0s
	1h 59m 37s

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