build: prepare for TypeScript 3.9 (#36989)

- Fix several compilation errors
- Update @microsoft/api-extractor to be compatible with TypeScript 3.9

PR Close #36989

packages/core/src/event_emitter.ts

@@ -61,7 +61,7 @@ import {Subject, Subscription} from 'rxjs';
  * @see [Observables in Angular](guide/observables-in-angular)
  * @publicApi
  */
-export class EventEmitter<T extends any> extends Subject<T> {
+export class EventEmitter<T> extends Subject<T> {
   /**
    * @internal
    */

packages/core/src/linker/element_ref.ts

@@ -24,7 +24,7 @@ import {noop} from '../util/noop';
 // Note: We don't expose things like `Injector`, `ViewContainer`, ... here,
 // i.e. users have to ask for what they need. With that, we can build better analysis tools
 // and could do better codegen in the future.
-export class ElementRef<T extends any = any> {
+export class ElementRef<T = any> {
   /**
    * The underlying native element or `null` if direct access to native elements is not supported
    * (e.g. when the application runs in a web worker).