React vendor script: avoid warning on createRoot (#76825)

* React vendor script: avoid warning on createRoot

* Fix broken build script

Co-authored-by: jsnajdr <jsnajdr@git.wordpress.org>
Co-authored-by: Mamaduka <mamaduka@git.wordpress.org>
Co-authored-by: aduth <aduth@git.wordpress.org>

Author: 3 people

bin/packages/build-vendors.mjs

@@ -22,6 +22,10 @@ const VENDOR_SCRIPTS = [
 		global: 'ReactDOM',
 		handle: 'react-dom',
 		dependencies: [ 'react' ],
+		contents: [
+			'export * from "react-dom";',
+			'export { createRoot, hydrateRoot } from "react-dom/client";',
+		].join( '\n' ),
 	},
 	{
 		name: 'react/jsx-runtime',
@@ -87,7 +91,7 @@ async function generateAssetFile( config ) {
  * @return {Promise<void>} Promise that resolves when all builds are finished.
  */
 async function bundleVendorScript( config ) {
-	const { name, global, handle } = config;
+	const { name, global, handle, contents } = config;
 
 	// Plugin that externalizes the `react` package.
 	const reactExternalPlugin = {
@@ -114,7 +118,6 @@ async function bundleVendorScript( config ) {
 	};
 
 	const esbuildOptions = {
-		entryPoints: [ name ],
 		bundle: true,
 		format: 'iife',
 		globalName: global,
@@ -123,6 +126,16 @@ async function bundleVendorScript( config ) {
 		plugins: [ reactExternalPlugin ],
 	};
 
+	if ( contents ) {
+		esbuildOptions.stdin = {
+			contents,
+			resolveDir: ROOT_DIR,
+			loader: 'js',
+		};
+	} else {
+		esbuildOptions.entryPoints = [ name ];
+	}
+
 	await Promise.all( [
 		esbuild.build( {
 			...esbuildOptions,
@@ -150,11 +163,11 @@ async function buildVendors() {
 			await bundleVendorScript( vendorConfig );
 			const buildTime = Date.now() - startTime;
 			console.log(
-				`   ✔ Bundled vendor ${ vendorConfig.name } (${ buildTime }ms)`
+				`   ✔ Bundled vendor ${ vendorConfig.handle } (${ buildTime }ms)`
 			);
 		} catch ( error ) {
 			console.error(
-				`   ✘ Failed to bundle vendor ${ vendorConfig.name }: ${ error.message }`
+				`   ✘ Failed to bundle vendor ${ vendorConfig.handle }: ${ error.message }`
 			);
 		}
 	}