common/build-style: add dune (OCaml builder)

[kwshi]

This PR defines a dune.sh build style to streamline OCaml builds using the Dune builder. Its purpose is analogous to the cargo build style for Rust projects, or python3-module build style for Python setup.py projects, etc.

As an example showing how it works, I've also added ocaml-sexplib0 (a common sexp library for OCaml), which builds using build_style=dune.

General

• This is a new package and it conforms to the quality requirements

Have the results of the proposed changes been tested?

• I use the packages affected by the proposed changes on a regular basis and confirm this PR works for me
• I generally don't use the affected packages but briefly tested this PR

[github-actions]

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