Implement `chmod` and `fchmod` for Unix targets #10095

Job	Run time
coverage report	5m 41s
style checks	45s
build (ubuntu-latest, x86_64-unknown-linux-gnu)	23m 54s
build (macos-14, aarch64-apple-darwin)	23m 18s
build (windows-latest, i686-pc-windows-msvc)	8m 38s
conclusion	1s
cronjob failure notification	0s
	1h 2m 17s

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