refactor(events): add deprecations (#19103)

angular/src/providers/events.ts

@@ -7,6 +7,11 @@ export type EventHandler = (...args: any[]) => any;
 export class Events {
   private c = new Map<string, EventHandler[]>();
 
+  constructor() {
+    console.warn(`[DEPRECATION][Events]: The Events provider is deprecated and it will be removed in the next major release.
+  - Use "Observables" for a similar pub/sub architecture: https://angular.io/guide/observables
+  - Use "Redux" for advanced state management: https://github.com/angular-redux/platform/tree/master/packages/store`);
+  }
   /**
    * Subscribe to an event topic. Events that get posted to that topic will trigger the provided handler.
    *