[core] Set isMap on properties that updatePropertyForMap turns into maps

[manduinca]

Fixes #25054

In an OpenAPI 3.1 spec, a property with additionalProperties and no type is an AnyType schema, so setTypeProperties marks it isAnyType and never isMap. fromProperty still sends it through updatePropertyForAnyType → updatePropertyForMap, which sets isContainer and containerType = "map" but leaves isMap false. The python from_dict template only has isArray and isMap branches inside isContainer, so the field matches neither and is dropped, which is the map=None from the issue. Serialization works because to_dict doesn't need the flag.

updatePropertyForMap now also sets isMap, the same way updateParameterForMap already does for parameters, so a property that is a map container is always flagged as one. For a schema that already had type: object this changes nothing, since isMap was already true. The new case is an untyped schema with additionalProperties (3.1 here, or an untyped composed schema with additionalProperties), which now carries isMap together with isAnyType in every generator, not only python.

Tests:

• DefaultCodegenTest#testUntypedMapPropertyIsMap: untyped, typed and $ref-valued map properties all come out with isMap. The untyped ones fail on master.
• PythonClientCodegenTest#testUntypedMapPropertyIsDeserialized: the generated from_dict reads map, typedMap and modelMap. Fails on master.
• Both use the new src/test/resources/3_1/issue_25054.yaml.

mvn test on modules/openapi-generator passes (5270 tests). ./bin/generate-samples.sh ./bin/configs/*.yaml (814 generators) and ./bin/utils/export_docs_generators.sh produce no changes, so no sample in the repo depends on the old behaviour.

cc Python technical committee: @cbornet @tomplus @krjakbrjak @fa0311

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Summary by cubic

updatePropertyForMap now sets isMap, matching what updateParameterForMap already does, so OpenAPI 3.1 properties with only additionalProperties are flagged as maps.

This fixes the Python client dropping such fields in from_dict, since the template only handles isArray and isMap inside isContainer. Typed object map properties are unaffected.

Tests:

• DefaultCodegenTest#testUntypedMapPropertyIsMap: untyped, typed and $ref-valued map properties all come out with isMap and containerType = "map"; the untyped ones fail on master.
• PythonClientCodegenTest#testUntypedMapPropertyIsDeserialized: the generated from_dict reads map, typedMap and modelMap as Dict[str, ...]; fails on master.
• Both use the new src/test/resources/3_1/issue_25054.yaml.

^{Written for commit 7842096. Summary will update on new commits.}

[cubic-dev-ai]

All reported issues were addressed across 4 files

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