os: expose `guessFileDescriptorType` #5194

Job	Run time
Build slim tarball	3m 4s
x86_64-darwin: with shared libraries	39m 12s
x86_64-linux: with shared libraries	21m 12s
aarch64-darwin: with shared libraries	20m 55s
aarch64-linux: with shared libraries	18m 6s
	1h 42m 29s

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