Don't expand defined types

This input will produce a schema where the type Result is not used in Response:

export type Result = { key: string };

export type Response = {
    items: { [name: string]: Result };
};

This is the output:

{
    "$schema": "http://json-schema.org/draft-07/schema#",
    "definitions": {
        "Response": {
            "properties": {
                "items": {
                    "additionalProperties": {
                        "properties": {
                            "key": {
                                "type": "string"
                            }
                        },
                        "type": "object"
                    },
                    "type": "object"
                }
            },
            "type": "object"
        },
        "Result": {
            "properties": {
                "key": {
                    "type": "string"
                }
            },
            "type": "object"
        }
    }
}

It works with interfaces:

export interface Result { key: string }

export interface Response {
    items: { [name: string]: Result };
}

Reproduce the issue with the TypeScript definitions shown in the report and inspect the schema-generation path that handles type aliases versus interfaces. Confirm that Response.items references Result in the generated schema rather than expanding it, while preserving the existing definitions output.