refactor(@angular-devkit/build-angular): disable requireContext parsing

`require.context` is a webpack specific feature which was only needed to support the old Karma test setup.

BREAKING CHANGE: `require.context` are no longer parsed. Webpack specific features are not supported nor guaranteed to work in the future.

Author: alan-agius4

Diff for: packages/angular_devkit/build_angular/src/webpack/configs/common.ts

@@ -342,8 +342,7 @@ export async function getCommonConfig(wco: WebpackConfigOptions): Promise<Config
       strictExportPresence: true,
       parser: {
         javascript: {
-          // TODO(alanagius): disable the below once we have a migration to remove `require.context` from test.ts file in users projects.
-          requireContext: true,
+          requireContext: false,
           // Disable auto URL asset module creation. This doesn't effect `new Worker(new URL(...))`
           // https://webpack.js.org/guides/asset-modules/#url-assets
           url: false,