Build both a partial renderer and fizz renderer of the legacy API for FB (#22933)

This lets us test how the new architecture performs without comparing it to
other infra changes related to streaming.

I renamed the streaming one to ReactDOMServerStreaming so the references
in www need to be updated.

I'll open an adhoc sync with just those files.

scripts/rollup/bundles.js

@@ -259,9 +259,14 @@ const bundles = [
 
   /******* React DOM Server *******/
   {
-    bundleTypes: __EXPERIMENTAL__
-      ? [UMD_DEV, UMD_PROD, NODE_DEV, NODE_PROD]
-      : [UMD_DEV, UMD_PROD, NODE_DEV, NODE_PROD, FB_WWW_DEV, FB_WWW_PROD],
+    bundleTypes: [
+      UMD_DEV,
+      UMD_PROD,
+      NODE_DEV,
+      NODE_PROD,
+      FB_WWW_DEV,
+      FB_WWW_PROD,
+    ],
     moduleType: RENDERER,
     entry: 'react-dom/src/server/ReactDOMLegacyServerBrowser',
     name: 'react-dom-server-legacy.browser',
@@ -317,7 +322,7 @@ const bundles = [
     bundleTypes: __EXPERIMENTAL__ ? [FB_WWW_DEV, FB_WWW_PROD] : [],
     moduleType: RENDERER,
     entry: 'react-server-dom-relay/src/ReactDOMServerFB',
-    global: 'ReactDOMServer',
+    global: 'ReactDOMServerStreaming',
     minifyWithProdErrorCodes: false,
     wrapWithModuleBoundaries: false,
     externals: ['react'],