fix(@angular-devkit/build-angular): don't process stylesheets in extraction builder

When building an application for i18n extraction we are currently redundantly processing components stylesheets. With this change we replace the components stylesheets with an empty string which helps reduce the i18n build time.

Author: alan-agius4

packages/angular_devkit/build_angular/src/extract-i18n/empty-export-default.js

@@ -0,0 +1 @@
+export default '';

packages/angular_devkit/build_angular/src/extract-i18n/index.ts

@@ -22,12 +22,7 @@ import { ExecutionTransformer } from '../transforms';
 import { createI18nOptions } from '../utils/i18n-options';
 import { assertCompatibleAngularVersion } from '../utils/version';
 import { generateBrowserWebpackConfigFromContext } from '../utils/webpack-browser-config';
-import {
-  getAotConfig,
-  getCommonConfig,
-  getStatsConfig,
-  getStylesConfig,
-} from '../webpack/configs';
+import { getAotConfig, getCommonConfig, getStatsConfig } from '../webpack/configs';
 import { createWebpackLoggingCallback } from '../webpack/utils/stats';
 import { Format, Schema } from './schema';
 
@@ -182,7 +177,6 @@ export async function execute(
         getCommonConfig(wco),
         // Only use VE extraction if not using Ivy
         getAotConfig(wco, !usingIvy),
-        getStylesConfig(wco),
         getStatsConfig(wco),
       ];
 
@@ -203,6 +197,16 @@ export async function execute(
         });
       }
 
+      // Replace all stylesheets with an empty default export
+      partials.push({
+        plugins: [
+          new webpack.NormalModuleReplacementPlugin(
+            /\.(css|scss|sass|styl|less)$/,
+            path.join(__dirname, 'empty-export-default.js'),
+          ),
+        ],
+      });
+
       return partials;
     },
   );
@@ -227,7 +231,7 @@ export async function execute(
     context,
     {
       logging: createWebpackLoggingCallback(false, context.logger),
-      webpackFactory: await import('webpack'),
+      webpackFactory: webpack,
     },
   ).toPromise();