Return statement: check that all control paths return a value

https://github.com/winglang/wing/blob/main/docs/04-reference/winglang-spec.md#24-return

Compiler should add a check that all control paths return a value

Example:

bring cloud;

resource WebHook {
  api: cloud.Api;

  init() {
    this.api = new cloud.Api();
    this.api.post("/", inflight (req: cloud.ApiRequest): cloud.ApiResponse => {
      log(Json.stringify(req));
    });
  }
}

The above code should error since the inflight does not return an api response.

Start with the return-statement section of docs/04-reference/winglang-spec.md linked in the issue and compare its requirements with the example. The work is done when the shown inflight function is rejected for lacking a return value while valid control paths that return an API response are accepted.