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>

spec/lib/js_locale_helper_spec.rb

@@ -4,7 +4,7 @@ require "mini_racer"
 
 RSpec.describe JsLocaleHelper do
   let(:v8_ctx) do
-    node_modules = "#{Rails.root}/app/assets/javascripts/node_modules/"
+    node_modules = "#{Rails.root}/node_modules/"
 
     transpiler = DiscourseJsProcessor::Transpiler.new
     discourse_i18n =