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

build-scripts/rollup-plugins/manifest-plugin.cjs

@@ -0,0 +1,34 @@
+const url = require("url");
+
+const defaultOptions = {
+  publicPath: "",
+};
+
+module.exports = function (userOptions = {}) {
+  const options = { ...defaultOptions, ...userOptions };
+
+  return {
+    name: "manifest",
+    generateBundle(outputOptions, bundle) {
+      const manifest = {};
+
+      for (const chunk of Object.values(bundle)) {
+        if (!chunk.isEntry) {
+          continue;
+        }
+        // Add js extension to mimic Webpack manifest.
+        manifest[`${chunk.name}.js`] = url.resolve(
+          options.publicPath,
+          chunk.fileName
+        );
+      }
+
+      this.emitFile({
+        type: "asset",
+        source: JSON.stringify(manifest, undefined, 2),
+        name: "manifest.json",
+        fileName: "manifest.json",
+      });
+    },
+  };
+};