[cpp-restsdk] Fix invalid code if type is referenced in schema

[mvistein-dlr]

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Problem

If a (primitive?) type is included in a schema per reference, invalid code is generated by cpp-restsdk. If the type is used directly, it is working as expected.

Example (working)

                    "apiKeyIds": {
                        "type": "array",
                        "readOnly": true,
                        "items": {
                            "type": "string",
                            "format": "uuid",
                            "readOnly": true
                        }
                    }

For this spec, the method getTypeDeclaration(...) in CppRestSdkClientCodegen.java will correctly return the type std::vector<utility::string_t>

Example (not working)

                    "apiKeyIds": {
                        "type": "array",
                        "items": {
                            "$ref": "#/components/schemas/UUID"
                        },
                        "readOnly": true
                    }

and UUID being defined as

           "UUID": {
                "format": "uuid",
                "pattern": "[a-fA-F0-9]{8}-[a-fA-F0-9]{4}-[a-fA-F0-9]{4}-[a-fA-F0-9]{4}-[a-fA-F0-9]{12}",
                "type": "string"
            },

This spec does no longer work with the cpp-restsdk because the type std::vector<std::shared_ptr<utility::string_t>> is generated. In a generated client there is an attempt to call from_json(...) on utility::string_t which obviously does not exist due to the additional shared pointer.

Fix

The suggested fix checks whether the referenced type is a known, built-in type and uses this type instead of wrapping it in a shared pointer.

I'm not 100% sure this is the right place to fix this.

This should also fix #8456