refactor(router): re-export the RouterTestingModule symbols

This commit re-exports the symbols that are exposed by the `RouterTestingModule` (which re-exports
the symbols from the `RouterModule`. These re-exports are needed for the Angular compiler
to overcome its limitation (on the consumer side) of not knowing where to import import
symbols when relative imports are used within the package.

Author: AndrewKushnir

packages/router/testing/src/testing.ts

@@ -13,3 +13,14 @@
  */
 export * from './router_testing_module';
 export {RouterTestingHarness} from './router_testing_harness';
+
+// Re-export the symbols that are exposed by the `RouterTestingModule` (which re-exports
+// the symbols from the `RouterModule`). Re-exports are needed for the Angular compiler
+// to overcome its limitation (on the consumer side) of not knowing where to import import
+// symbols when relative imports are used within the package.
+// Note: These exports need to be stable and shouldn't be renamed unnecessarily because
+// consuming libraries might have references to them in their own partial compilation output.
+export {RouterOutlet as ɵɵRouterOutlet} from '../../src/directives/router_outlet';
+export {RouterLink as ɵɵRouterLink} from '../../src/directives/router_link';
+export {RouterLinkActive as ɵɵRouterLinkActive} from '../../src/directives/router_link_active';
+export {EmptyOutletComponent as ɵɵEmptyOutletComponent} from '../../src/components/empty_outlet';