fix(common): correct mapping of Observable methods (#20518)

fixes #20516 PR Close #20518

Author: trotyl

packages/common/http/rollup.config.js

@@ -14,7 +14,7 @@ const globals = {
  'rxjs/Observer': 'Rx',
  'rxjs/Subject': 'Rx',
 
- 'rxjs/observable/of': 'Rx.Observable.prototype',
+ 'rxjs/observable/of': 'Rx.Observable',
 
  'rxjs/operator/concatMap': 'Rx.Observable.prototype',
  'rxjs/operator/filter': 'Rx.Observable.prototype',