[Fix][OCaml] Incorrect encoding/decoding for required free-form objects; Odoc for record fields

[sir4ur0n]

This MR fixes:

• I noticed that encoding/decoding was incorrect for free-form objects, so here is the fix, together with a new test for good measure (I was surprised that the generic fake petstore did not have a required free-form object, and I did not dare add it because it would change many samples outside of OCaml)
• the ocaml-oneOf was incorrectly named, so I cleaned this mess I created in an earlier MR 😅
• a minor fix where record fields now use the Odoc syntax (and thus are moved after the field). OCaml documentation requires 2 stars (*) to be valid documentation. It also means that now field documentation is visible via LSP (see screenshot below)
• remove some files in the ocaml sample that were not actually generated by the spec

@cgensoul @wing328

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[wing328]

thanks for the pr

let's give it a try

[wing328]

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