hash function in modules Bool/Int/Char/String

[backtracking]

It would be convenient if modules Bool/Int/Char/String would provide a hash function, so that we can pass them to functors such as Hashtbl.Make.

Of course, we can use the polymorphic hash function Hashtbl.hash for this purpose, or define custom hash function (e.g. the identity for type int), but that's less convenient from a user's perspective.

Note: module Float already provides a hash function.

[dra27]

Cross-referencing at least https://github.com/ocaml/ocaml/pull/8878/files (String.hash)

[xavierleroy]

See my comment here: #10262 (comment) . There's a tension between seeded and unseeded hash functions, and bad name choices in the past prevent us from implementing both in the same module.

[github-actions]

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