Implement `chmod` and `fchmod` for Unix targets #10091

Job	Run time
style checks	2m 4s
build (ubuntu-latest, x86_64-unknown-linux-gnu)	26m 13s
coverage report	7m 10s
build (macos-14, aarch64-apple-darwin)	29m 8s
build (windows-latest, i686-pc-windows-msvc)	7m 7s
conclusion	1s
cronjob failure notification	0s
	1h 11m 43s

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