Default values and patter/length checks are not inherrited

[Leptopoda]

When generating a schema that inherits parameters from a super schema the builtvalue _initialize and _finalize hooks will not be included in the subschema.

            "SuperObject": {
                "type": "object",
                "properties": {
                    "value": {
                        "type": "string",
                        "pattern": "^[0-9]*$",
                        "minLength": 3,
                        "maxLength": 20,
                        "default": "123"
                    }
                },
                "required": [
                    "value"
                ]
            },
            "SubObject": {
                "type": "object",
                "allOf": [
                    {
                        "$ref": "#/components/schemas/SuperObject"
                    }
                ]
            }

[provokateurin]

google/built_value.dart#1310 for reference