perf(http-loader): use of httpBackend

[rbalet]

Current behavior

The http-loader is using httpClient, which get blocked by the Interceptor.
This does create several issues.

Expected behavior

Enabling the use of HttpBackend

[CodeAndWeb]

73c8a27

Implements a static function that can be used to create the loader with a backend:
TranslateHttpLoader.withHttpBackend(httpBackend, '/assets/i18n/', '.json'),

I decided to remove that again and update the documentation instead. Users can easily make the choice to pass in the HttpBackend in the factory method as mentioned here: #1312

 provideTranslateService({
          loader: {
            provide: TranslateLoader,
            useFactory: (httpBackend: HttpBackend) =>
              new TranslateHttpLoader(new HttpClient(httpBackend), '/assets/i18n/', '.json'),
            deps: [HttpBackend],
          }
        }),

Adding that functionality in the library as a separate function would only bloat the code without much benefit for the users since they have to change he dependencies anyways. So it's just wrapping the parameter with new HttpClient()

The users requiring this would only save characters... so there's not really a big use for introducing a new function.

TranslateHttpLoader.withHttpBackend(httpBackend, '/assets/i18n/', '.json'),

vs

new TranslateHttpLoader(new HttpClient(httpBackend), '/assets/i18n/', '.json'),