Build: Add work-around for safari 10 let bug (#26068)

* Build: Add work-around for safari 10 let bug

See mishoo/UglifyJS#1851

* Add the mangle option to the right minifier. Remove the redundant one.

* change the opt extension to min to cache break the uglify change

webpack.config.js

@@ -83,8 +83,8 @@ const webpackConfig = {
 	output: {
 		path: path.join( __dirname, 'public' ),
 		publicPath: '/calypso/',
-		filename: '[name].[chunkhash].opt.js', // prefer the chunkhash, which depends on the chunk, not the entire build
-		chunkFilename: '[name].[chunkhash].opt.js', // ditto
+		filename: '[name].[chunkhash].min.js', // prefer the chunkhash, which depends on the chunk, not the entire build
+		chunkFilename: '[name].[chunkhash].min.js', // ditto
 		devtoolModuleFilenameTemplate: 'app:///[resource-path]',
 	},
 	optimization: {
@@ -112,6 +112,9 @@ const webpackConfig = {
 						 */
 						collapse_vars: false,
 					},
+					mangle: {
+						safari10: true,
+					},
 					ecma: 5,
 				},
 			} ),
@@ -254,25 +257,4 @@ if ( ! config.isEnabled( 'desktop' ) ) {
 	);
 }
 
-if ( shouldMinify ) {
-	webpackConfig.plugins.push(
-		new UglifyJsPlugin( {
-			cache: 'docker' !== process.env.CONTAINER,
-			parallel: true,
-			sourceMap: Boolean( process.env.SOURCEMAP ),
-			uglifyOptions: {
-				compress: {
-					/**
-					 * Produces inconsistent results
-					 * Enable when the following is resolved:
-					 * https://github.com/mishoo/UglifyJS2/issues/3010
-					 */
-					collapse_vars: false,
-				},
-				ecma: 5,
-			},
-		} )
-	);
-}
-
 module.exports = webpackConfig;