tree shaking support for services (#3906)

[ADF-3697] tree shaking support for services

lib/core/context-menu/context-menu-overlay.service.ts

@@ -29,7 +29,9 @@ const DEFAULT_CONFIG: ContextMenuOverlayConfig = {
     hasBackdrop: true
 };
 
-@Injectable()
+@Injectable({
+    providedIn: 'root'
+})
 export class ContextMenuOverlayService {
 
     constructor( private injector: Injector, private overlay: Overlay) { }

lib/core/context-menu/context-menu.service.ts

@@ -18,7 +18,9 @@
 import { Injectable } from '@angular/core';
 import { Subject } from 'rxjs';
 
-@Injectable()
+@Injectable({
+    providedIn: 'root'
+})
 export class ContextMenuService {
     public show: Subject<{event: MouseEvent, obj: any[]}> = new Subject<{event: MouseEvent, obj: any[]}>();
 }