DEV: Use esbuild to make DiscourseJsProcessor (#23223)

Reverts e2705df and re-lands #23187 and #23219.

The issue was incorrect order of execution of Rails' `assets:precompile` task in our own precompilation stack.

Co-authored-by: David Taylor <david@taylorhq.com>

spec/lib/discourse_js_processor_spec.rb

@@ -155,7 +155,7 @@ RSpec.describe DiscourseJsProcessor do
       Handlebars.registerHelper('dummy-helper', function(string) {
         return `dummy(${string})`
       })
-      JS
+    JS
 
     let(:mini_racer) do
       ctx = MiniRacer::Context.new