fix: polyfill global.Node for angular testing (#2340)

Author: edusperoni

nativescript-angular/testing/src/polyfills.ts

@@ -0,0 +1,4 @@
+if (typeof Node === 'undefined' && !global.Node) {
+	class DummyNode {}
+	global.Node = DummyNode as any;
+}

nativescript-angular/testing/src/public_api.ts

@@ -1,3 +1,4 @@
+import './polyfills';
 export * from './util';
 export * from './test-root-view';
 export * from './nativescript_test_component_renderer';