[BUG] Typescript-rxjs: api client instance created with withMiddleware() does not use new middlewares

Bug Report Checklist

• Have you provided a full/minimal spec to reproduce the issue?
• Have you validated the input using an OpenAPI validator (example)?
• Have you tested with the latest master to confirm the issue still exists?
• Have you searched for related issues/PRs?
• What's the actual output vs expected output?
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Description

When creating new SomeApi instance like const newInstance = someApiInstance.withMiddleware(middlewares), the provided middlewares are not used by new instance.

This is because some methods, including rxjsRequest(), are defined as arrow functions and are copied to new instance in clone(). With current code, the methods in the new instance alway reads middleware of some old instance (this when creating the arrow functions).

IMO the current behavior effectively removed the meaning of withMiddleware().

openapi-generator version

generator-cli v4.3.1 (the problem still exists in master)

Related issues/PRs

They were changed to current form in https://github.com/OpenAPITools/openapi-generator/pull/3077/files , seemingly to save bytes.

Suggest a fix

Changing clone method to use new (like in typescript-fetch ) should fix it.

Start by locating the TypeScript-RxJS runtime and its clone() implementation, then compare it with samples/client/petstore/typescript-fetch/builds/es6-target/src/runtime.ts. Reproduce the withMiddleware() case and verify that methods on the new client use the supplied middleware rather than the original instance's middleware.