Fix actiontext js not pointing to compiled file

This caused issues with bundlers like Webpack since it tries to strictly
follow the ESM spec which says that imports must include file
extensions.

Author: skipkayhil

actiontext/package.json

@@ -2,10 +2,10 @@
   "name": "@rails/actiontext",
   "version": "7.1.0-alpha",
   "description": "Edit and display rich text in Rails applications",
-  "main": "app/javascript/actiontext/index.js",
+  "main": "app/assets/javascripts/actiontext.js",
   "type": "module",
   "files": [
-    "app/javascript/actiontext/*.js"
+    "app/assets/javascripts/*.js"
   ],
   "homepage": "https://rubyonrails.org/",
   "repository": {