Add Node ESM Loader and Register Entrypoints (#20274)

* Add Node ESM loader build

This adds a loader build as a first-class export. This will grow in
complexity so it deserves its own module.

* Add Node CommonJS regiter build

This adds a build as a first-class export for legacy CommonJS registration
in Node.js. This will grow in complexity so it deserves its own module.

* Simplify fixture a bit to easier show usage with or without esm

* Bump es version

We leave async function in here which are newer than ES2015.

scripts/shared/pathsByLanguageVersion.js

@@ -10,6 +10,7 @@
 const esNextPaths = [
   // Internal forwarding modules
   'packages/*/*.js',
+  'packages/*/esm/*.js',
   // Source files
   'packages/*/src/**/*.js',
   'packages/dom-event-testing-library/**/*.js',