Use String.split_on_char. #11826

Job	Run time
build_details	2s
build_js	2m 1s
build_opam (4.14.x)	8m 55s
build_opam (5.2.x)	5m 16s
lezer_parse	50s
build_no_depopts	5m 55s
tree_sitter_parse	51s
build_posix (debian_trixie, amd64)	14m 21s
build_win32 (x64)	17m 46s
build_posix (debian_bookworm, amd64)	14m 10s
run_tests (@citest)	12m 50s
update_doc	11m 55s
build_posix (ubuntu_oracular, amd64)	15m 55s
run_tests (@doctest)	8m 0s
build_posix (ubuntu_noble, amd64)	14m 17s
run_tests (@mediatest)	13m 1s
build_posix (alpine, amd64)	11m 53s
fetch_s3_artifacts	20s
build_docker_minimal (amd64)	3m 9s
build_docker_alpine_minimal (amd64)	47s
build_docker_alpine (amd64)	1m 33s
build_docker (amd64)	2m 22s
update_release	0s
build_docker_release	0s
build_docker_release-minimal	0s
	2h 46m 9s

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