docs: document any_changed, all_changed helpers for _if #1574

Job	Run time
spell-check	3s
type-check	18s
lint	19s
unit-test (ubuntu-20.04, 3.8)	40s
unit-test (ubuntu-20.04, 3.9)	37s
end-to-end-test (ubuntu-20.04, local)	24s
unit-test (ubuntu-20.04, 3.10)	33s
end-to-end-test (ubuntu-20.04, ssh)	1m 16s
unit-test (ubuntu-20.04, 3.11)	35s
end-to-end-test (ubuntu-20.04, docker)	26s
unit-test (ubuntu-20.04, 3.12)	44s
end-to-end-test (ubuntu-latest, local)	22s
unit-test (ubuntu-latest, 3.8)	38s
end-to-end-test (ubuntu-latest, ssh)	1m 17s
unit-test (ubuntu-latest, 3.9)	33s
end-to-end-test (ubuntu-latest, docker)	23s
unit-test (ubuntu-latest, 3.10)	33s
end-to-end-test (macos-latest, local)	19s
unit-test (ubuntu-latest, 3.11)	32s
unit-test (ubuntu-latest, 3.12)	42s
unit-test (macos-13, 3.11)	1m 1s
unit-test (windows-2022, 3.11)	1m 13s
tests-done	1s
	13m 29s

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