docs: include additional interfaces to 'rxjs' export site

[jakovljevic-mladen]

Description:
With #6391, a couple of existing interfaces got exported publicly. Now, since that PR was made before operators have been exported from 'rxjs' export site as well, all those interfaces got exported from 'rxjs/operators'. I am now exporting this from 'rxjs' as well, so that users can have this:

import { throttle, ThrottleConfig } from 'rxjs';

instead of:

import { throttle } from 'rxjs';
import { ThrottleConfig } from 'rxjs/operators';

Related issue (if exists):
None, just a question where I asked to do this in the first place, but the question has never been answered before #6391 was merged.