chore(*): Add es2019 lib and remove unused imports

Author: dkamburov

projects/igniteui-angular/src/lib/grids/pivot-grid/pivot-grid.component.ts

@@ -23,9 +23,7 @@ import {
     ViewContainerRef,
     Injector,
     NgModuleRef,
-    ApplicationRef,
-    ContentChildren
-} from '@angular/core';
+    ApplicationRef} from '@angular/core';
 import { IgxGridBaseDirective } from '../grid-base.directive';
 import { IgxFilteringService } from '../filtering/grid-filtering.service';
 import { IgxGridSelectionService } from '../selection/selection.service';
@@ -55,7 +53,7 @@ import { IgxPivotColumnResizingService } from '../resizing/pivot-grid/pivot-resi
 import { IgxFlatTransactionFactory, IgxOverlayService, State, Transaction, TransactionService } from '../../services/public_api';
 import { DOCUMENT } from '@angular/common';
 import { DisplayDensityToken, IDisplayDensityOptions } from '../../core/displayDensity';
-import { cloneArray, flatten, PlatformUtil } from '../../core/utils';
+import { cloneArray, PlatformUtil } from '../../core/utils';
 import { IgxPivotFilteringService } from './pivot-filtering.service';
 import { DataUtil } from '../../data-operations/data-util';
 import { IFilteringExpressionsTree } from '../../data-operations/filtering-expressions-tree';

projects/igniteui-angular/tsconfig.lib.json

@@ -17,7 +17,8 @@
     "lib": [
       "dom",
       "es2015",
-      "es2017"
+      "es2017",
+      "es2019"
     ]
   },
   "angularCompilerOptions": {