fix using actiontext.js in sprocket

actiontext.js is compiled as ESM bundle instead of UMD bundle.
This leads to issues when trying to use ActionText with sprockets because the ESM bundle declares variables like they are scoped to the file but sprockets will see them as scoped globally.
This is a problem, in particular, if you want to mix actiontext with
turbo-rails.

The problem got introduced in rails#46447.
I traced valid compilation back to
rails#42895.

This commit mimic changes made in
rails#42895 to ActiveStorage:
   Retains app/assets/javascripts/actiontext.js as a UMD package for backwards compatibility with
   bundling in the asset pipeline, but also adds app/assets/javascripts/actiontext.esm.js for use
   with ESM via importmap in the browser.

actiontext/CHANGELOG.md

@@ -1,3 +1,11 @@
+*   Compile ESM package that can be used directly in the browser as actiontext.esm.js
+
+    *Matias Grunberg*
+
+*   Fix using actiontext.js with Sprockets
+
+    *Matias Grunberg*
+
 *   Upgrade Trix to 2.0.7
 
     *Hartley McGuire*

actiontext/app/assets/javascripts/.gitattributes

@@ -1,2 +1,3 @@
 actiontext.js linguist-generated
+actiontext.esm.js linguist-generated
 trix.js linguist-vendored