[BUG] [typescript] not compatible with --isolatedModules

Bug Report Checklist

• Have you provided a full/minimal spec to reproduce the issue?
• Have you validated the input using an OpenAPI validator (example)?
• What's the version of OpenAPI Generator used?
• Have you search for related issues/PRs?
• What's the actual output vs expected output?
• [Optional] Bounty to sponsor the fix (example)

Description

Using the new TypeScript generator from #6341

The generated code is not compatible with --isolatedModules, which is required by popular setups such as create-react-app.

openapi-generator version

5.0.0-SNAPSHOT

OpenAPI declaration file content or url

https://github.com/bard/repro-openapi-generator-typescript-isolated-modules/blob/master/example.yaml

Command line used for generation

OPENAPI_GENERATOR_VERSION=5.0.0-SNAPSHOT /tmp/openapi-generator-cli.sh generate -g typescript -i example.yaml -o ./src/api

Steps to reproduce

1. git clone https://github.com/bard/repro-openapi-generator-typescript-isolated-modules/blob/master/example.yaml
2. OPENAPI_GENERATOR_VERSION=5.0.0-SNAPSHOT /tmp/openapi-generator-cli.sh generate -g typescript -i example.yaml -o ./src/api
3. yarn && yarn start

Failed to compile.

/tmp/repro-openapi-generator-typescript-isolated-modules/src/api/index.ts
TypeScript error in /tmp/repro-openapi-generator-typescript-isolated-modules/src/api/index.ts(4,31):
Cannot re-export a type when the '--isolatedModules' flag is provided.  TS1205

    2 | export * from "./auth/auth";
    3 | export * from "./models/all";
  > 4 | export { createConfiguration, Configuration } from "./configuration"
      |                               ^
    5 | export * from "./apis/exception";
    6 | export * from "./servers";
    7 | 

Related issues/PRs

https://github.com/facebook/create-react-app/issues/6054

Suggest a fix

Possible workaround is to export * from index.ts:

  export * from "./http/http";
  export * from "./auth/auth";
  export * from "./models/all";
- export { createConfiguration, Configuration } from "./configuration"
+ export * from "./configuration"
  export * from "./apis/exception";
  export * from "./servers";

Start with the generated src/api/index.ts shown in the report and reproduce the failure using the provided OpenAPI declaration, generator command, and yarn start steps. Trace that output back to the TypeScript generator templates or entry points, then verify that regenerated code compiles with --isolatedModules without the TS1205 error.