fix(@angular-devkit/build-angular): explicitly set compilation target…

… in test configuration

When not set, and browserslist returns no reesults due to the file being empty or commented. Webpack will generate invalid code because it doesn't know which enviorment we want to target.

```diff
- (self["webpackChunktest_app"] = self["webpackChunktest_app"] || []).push([["vendor"],{

/***/ 8583:
```

Closes #21111

packages/angular_devkit/build_angular/src/webpack/configs/test.ts

@@ -8,6 +8,7 @@
 
 import * as glob from 'glob';
 import * as path from 'path';
+import { ScriptTarget } from 'typescript';
 import * as webpack from 'webpack';
 import { WebpackConfigOptions, WebpackTestOptions } from '../../utils/build-options';
 import { getSourceMapDevTool, isPolyfillsEntry } from '../utils/helpers';
@@ -51,6 +52,7 @@ export function getTestConfig(
 
   return {
     mode: 'development',
+    target: wco.tsConfig.options.target === ScriptTarget.ES5 ? ['web', 'es5'] : 'web',
     resolve: {
       mainFields: ['es2015', 'browser', 'module', 'main'],
     },