[OCaml] Introduce support for oneOf/anyOf, fix default value for non-required maps (#21798)

* Add OCaml fake-petstore to test corner cases

* Prefix List functions with Stdlib as the fake petstore generates a List module

* Handle decimal and any types

* Indent to_json.mustache for easier maintenance

* Indent api-impl.mustache a bit more for readability before fix

* Fix: do not call `to_json` for free forms and byte arrays

Fixes https://github.com/OpenAPITools/openapi-generator/issues/21312

* Fix compilation for binary types

The implementation may not be correct, but at least it compiles. To be checked
if someday someone actually uses it/complains.

* Indent to_string.mustache

* Add support for exploded form-style object query params

Fixes https://github.com/OpenAPITools/openapi-generator/issues/21307

* Add ocaml-fake-petstore to CI

* Fix free-form body params

* Cohttp_lwt.Response is deprecated, use Cohttp.Response instead

* Safe Java code cleanup

* Split into model-record.mustache

* Add some support for oneOf/anyOf

* Re-generate all OCaml samples

* Fix: correctly mark non-required maps with default empty list

* Fix: Correctly encode/decode maps

* Refresh documentation

* Refresh after merging master

.github/workflows/samples-ocaml.yaml

@@ -4,9 +4,13 @@ on:
   push:
     paths:
       - 'samples/client/petstore/ocaml/**'
+      - 'samples/client/petstore/ocaml-fake-petstore/**'
+      - 'samples/client/petstore/ocaml-oneOf/**'
   pull_request:
     paths:
       - 'samples/client/petstore/ocaml/**'
+      - 'samples/client/petstore/ocaml-fake-petstore/**'
+      - 'samples/client/petstore/ocaml-oneOf/**'
 
 jobs:
   build:
@@ -17,6 +21,8 @@ jobs:
       matrix:
         sample:
           - 'samples/client/petstore/ocaml/'
+          - 'samples/client/petstore/ocaml-fake-petstore/'
+          - 'samples/client/petstore/ocaml-oneOf/'
     steps:
       - uses: actions/checkout@v5
       - name: Set-up OCaml