[playground] Turn on Forget

Runs Forget on the playground, so we can dogfood Forget and experiment with 
improvements to UX. 

Opts out of compiling the layout page because thats run on the server which 
doesn't seem to have access to useMemoCache.

compiler/apps/playground/app/layout.tsx

@@ -12,6 +12,7 @@ export default function RootLayout({
 }: {
   children: React.ReactNode;
 }) {
+  "use no forget";
   return (
     <html lang="en">
       <head>

compiler/apps/playground/babel.config.js

@@ -0,0 +1,16 @@
+module.exports = function (api) {
+  api.cache(true);
+  return {
+    presets: ["next/babel"],
+    plugins: [
+      [
+        "babel-plugin-react-forget",
+        {
+          gating: null,
+          compilationMode: "infer",
+          panicThreshold: "NONE",
+        },
+      ],
+    ],
+  };
+};