refactor(EventEmitter): rename .next() to .emit()

BREAKING CHANGE:

EventEmitter#next(value) is deprecated, use EventEmitter#emit(value)
instead.

Closes #4287

Closes #5302

modules/playground/src/order_management/index.ts

@@ -147,7 +147,7 @@ class OrderItemComponent {
   @Input() item: OrderItem;
   @Output() delete = new EventEmitter();
 
-  onDelete(): void { this.delete.next(this.item); }
+  onDelete(): void { this.delete.emit(this.item); }
 }
 
 @Component({

modules/playground/src/upgrade/index.ts

@@ -54,7 +54,7 @@ class Pane {
         <table cellpadding="3">
           <tr>
             <td><ng-content></ng-content></td>
-            <td><user [handle]="user" (reset)="reset.next()"></user></td>
+            <td><user [handle]="user" (reset)="reset.emit()"></user></td>
           </tr>
         </table>
       </pane>

modules/playground/src/zippy_component/zippy.ts

@@ -11,9 +11,9 @@ export class Zippy {
   toggle() {
     this.visible = !this.visible;
     if (this.visible) {
-      ObservableWrapper.callNext(this.open, null);
+      ObservableWrapper.callEmit(this.open, null);
     } else {
-      ObservableWrapper.callNext(this.close, null);
+      ObservableWrapper.callEmit(this.close, null);
     }
   }
 }