Fix ES5 build, fix virtualizer polyfill (#7451)

build-scripts/webpack.js

@@ -51,9 +51,6 @@ const createWebpackConfig = ({
         }),
       ],
     },
-    experiments: {
-      topLevelAwait: true,
-    },
     plugins: [
       new ManifestPlugin({
         // Only include the JS of entrypoints
@@ -98,6 +95,15 @@ const createWebpackConfig = ({
         new RegExp(bundle.emptyPackages({ latestBuild }).join("|")),
         path.resolve(paths.polymer_dir, "src/util/empty.js")
       ),
+      // We need to change the import of the polyfill for EventTarget, so we replace the polyfill file with our customized one
+      new webpack.NormalModuleReplacementPlugin(
+        new RegExp(
+          require.resolve(
+            "lit-virtualizer/lib/uni-virtualizer/lib/polyfillLoaders/EventTarget.js"
+          )
+        ),
+        path.resolve(paths.polymer_dir, "src/resources/EventTarget-ponyfill.js")
+      ),
     ],
     resolve: {
       extensions: [".ts", ".js", ".json"],