Replace NgModule approach by provide function

[rlexa]

Angular moved on to functional providers approach (EnvironmentProviders), please replace NgModule by an appropriate provide function.

Right now it has to be provided with a helper function from Angular:

bootstrapApplication(AppComponent, {
    providers: [
      importProvidersFrom(ApiModule.forRoot({rootUrl: BACKEND_PATH})),
...

Instead the code could be generated like:

@Injectable({providedIn: 'root'})
export class ApiConfiguration {
  rootUrl?: string;
}

export const apiConfigurationGenerated: ApiConfiguration = {rootUrl: '/api'};

export function provideNgOpenapi(params: ApiConfigurationParams) {
  return makeEnvironmentProviders([
    SomeGeneratedService,
    OtherGeneratedService,
    {provide: ApiConfiguration, useValue: {...apiConfigurationGenerated, ...params}},
  ]);
}

With environment providers there is no need for already-exists checking. This allows for modern approach:

bootstrapApplication(AppComponent, {
    providers: [
      provideNgOpenapi({rootUrl: BACKEND_PATH}),
...

[mumenthalers]

@rlexa missed this issue and created a separate one #342, with the same goal but a non-breaking approach by using a standalone option.
Naming can be discussed, but for sure it is the logical way to go.