chore(tree): implement ngOnDestroy hook in nav service to prevent memory leak

Author: ViktorSlavov

projects/igniteui-angular/src/lib/tree/tree-navigation.service.ts

@@ -1,12 +1,12 @@
-import { Injectable } from '@angular/core';
+import { Injectable, OnDestroy } from '@angular/core';
 import { IgxTree, IgxTreeNode, IGX_TREE_SELECTION_TYPE } from './common';
 import { NAVIGATION_KEYS } from '../core/utils';
 import { IgxTreeService } from './tree.service';
 import { IgxTreeSelectionService } from './tree-selection.service';
 import { Subject } from 'rxjs';
 
 @Injectable()
-export class IgxTreeNavigationService {
+export class IgxTreeNavigationService implements OnDestroy {
     private tree: IgxTree;
 
     private _focusedNode: IgxTreeNode<any> = null;
@@ -131,6 +131,11 @@ export class IgxTreeNavigationService {
         }
     }
 
+    public ngOnDestroy() {
+        this._cacheChange.next();
+        this._cacheChange.complete();
+    }
+
     private handleNavigation(event: KeyboardEvent) {
         switch (event.key.toLowerCase()) {
             case 'home':