Make module types explicit and convert some to ESM (#15964)

webpack.config.cjs

@@ -0,0 +1,28 @@
+/* eslint-disable @typescript-eslint/no-var-requires */
+// Needs to remain CommonJS until eslint-import-resolver-webpack supports ES modules
+const webpack = require("./build-scripts/webpack.cjs");
+const env = require("./build-scripts/env.cjs");
+
+// This file exists because we haven't migrated the stats script yet
+
+const configs = [
+  webpack.createAppConfig({
+    isProdBuild: env.isProdBuild(),
+    isStatsBuild: env.isStatsBuild(),
+    isTestBuild: env.isTestBuild(),
+    latestBuild: true,
+  }),
+];
+
+if (env.isProdBuild() && !env.isStatsBuild()) {
+  configs.push(
+    webpack.createAppConfig({
+      isProdBuild: env.isProdBuild(),
+      isStatsBuild: env.isStatsBuild(),
+      isTestBuild: env.isTestBuild(),
+      latestBuild: false,
+    })
+  );
+}
+
+module.exports = configs;