chore(sample): set --ig-theme instead of importing the stylesheet

Author: didimmova

samples/grids/grid/advanced-filtering-style/src/index.css

@@ -1,6 +1,10 @@
 /* shared styles are loaded from: */
 /* https://dl.infragistics.com/x/css/samples/shared.v8.css */
 
+:root {
+    --ig-theme: bootstrap;
+}
+
 #grid {
     --ig-query-builder-header-foreground: #512da8;
     --ig-query-builder-color-expression-group-and: #eb0000;
@@ -9,4 +13,3 @@
     --ig-query-builder-subquery-border-color: var(--ig-warn-500);
     --ig-query-builder-subquery-border-radius: 4px;
 }
-

samples/grids/grid/advanced-filtering-style/src/index.ts

@@ -1,4 +1,3 @@
-import "igniteui-webcomponents/themes/light/bootstrap.css";
 import "igniteui-webcomponents-grids/grids/themes/light/bootstrap.css";
 import 'igniteui-webcomponents-grids/grids/combined';
 import { ComponentRenderer, WebGridDescriptionModule } from 'igniteui-webcomponents-core';