Increase discoverability of `merge_join_by` (Unix-like `comm`) #1018

Job	Run time
check	9s
test	50s
check (--no-default-features)	7s
msrv	24s
check (--no-default-features --features use_alloc)	21s
check (--all-targets --all-features)	23s
check format	6s
doc	9s
miri	3m 32s
semver-checks	10s
All checks succeeded	1s
	6m 12s

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