add new generator: typescript-rxjs

[denyo]

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Description of the PR

This PR adds a new generator typescript-rxjs which is based on typescript-fetch and replaces all fetch and Promise related things with rxjs ajax and Observables: https://github.com/ReactiveX/rxjs/blob/master/src/internal/observable/dom/AjaxObservable.ts.

[wing328]

cc @TiFu (2017/07) @taxpon (2017/07) @sebastianhaas (2017/07) @kenisteward (2017/07) @Vrolijkx (2017/09) @macjohnny (2018/01) @nicokoenig (2018/09) @topce (2018/10)

[macjohnny]

see also #802 (comment)

[macjohnny]

@denyo I suggest you to add an entry to
https://github.com/openapitools/openapi-generator/blob/master/bin/utils/ensure-up-to-date#L31

also, it would be good to have a small integration test to avoid regression issues. see e.g.
https://github.com/OpenAPITools/openapi-generator/blob/master/pom.xml#L1074

https://github.com/OpenAPITools/openapi-generator/blob/master/samples/client/petstore/typescript-angular-v6-provided-in-root/pom.xml

https://github.com/OpenAPITools/openapi-generator/tree/master/samples/client/petstore/typescript-angular-v6-provided-in-root/tests/default

[denyo]

@macjohnny thanks for the feedback and hints.
I applied the small changes. However I won't have the time to add tests or anything. So if this is required then I would need someone else to jump in and continue from here.

[macjohnny]

the interface RequestInit seems to be missing.

[denyo]

Thanks for the additions.
RequestInit is part of typescript itself.

[macjohnny]

RequestInit is part of typescript itself.

You are right, I missed that. So you can revert the change I suggested that adds the interface AjaxRequestParts

[denyo]

Will do. Also the one with return throwError(res) causes problems:

Type error: Type 'Observable<Observable<never> | T>' is not assignable to type 'Observable<T>'.
  Type 'Observable<never> | T' is not assignable to type 'T'.
    Type 'Observable<never>' is not assignable to type 'T'.  TS2322

    44 | 
    45 |     protected request<T>(context: RequestOpts): Observable<T> {
  > 46 |         return this.rxjsRequest(this.createRequestArgs(context)).pipe(
       |         ^
    47 |             map((res) => {
    48 |                 if (res.status >= 200 && res.status < 300) {
    49 |                     return res.response as T;

[macjohnny]

Also the one with return throwError(res) causes problems:

you are right, it is inside a map operator, not switchMap. Sorry for that

[wing328]

@denyo thanks for the PR, which has been merged into master.

@macjohnny thanks for reviewing the change.