DEV: Merge root JS packages (#25857)

Before this commit, we had a yarn package set up in the root directory and also in `app/assets/javascripts`. That meant two `yarn install` calls and two `node_modules` directories. This commit merges them both into the root location, and updates references to node_modules.

A previous attempt can be found at https://github.com/discourse/discourse/pull/21172. This commit re-uses that script to merge the `yarn.lock` files.

Co-authored-by: Jarek Radosz <jradosz@gmail.com>

lib/js_locale_helper.rb

@@ -332,9 +332,7 @@ module JsLocaleHelper
         @ctx ||=
           begin
             ctx = MiniRacer::Context.new(timeout: 15_000, ensure_gc_after_idle: 2000)
-            ctx.load(
-              "#{Rails.root}/app/assets/javascripts/node_modules/messageformat/messageformat.js",
-            )
+            ctx.load("#{Rails.root}/node_modules/messageformat/messageformat.js")
             ctx
           end
       )