Support `rescript.json` #222

Job	Run time
build (macos-13, rescript)	11m 27s
build (macos-14, rescript)	6m 50s
build (ubuntu-latest, rescript)	5m 58s
build (windows-latest, rescript)	10m 40s
build (ubuntu-latest, ocaml.4.08, 4.08.x, opam exec -- dune build)	6m 10s
build (ubuntu-latest, ocaml.4.14, 4.14.x, opam exec -- dune build)	5m 55s
build (ubuntu-latest, ocaml.5.0, 5.0.x, opam exec -- dune build)	5m 51s
build (ubuntu-latest, ocaml.5.1, 5.1.x, opam exec -- dune build)	5m 50s
npm_pack	22s
	59m 3s

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