DEV: Improve strategy for identifying ember-cli JS chunks (#23336)

Our Ember build compiles assets into multiple chunks. In the past, we used the output from `ember-auto-import-chunks-json-generator` to give Rails a map of those chunks. However, that addon is specific to ember-auto-import, and is not compatible with Embroider.

Instead, we can switch to parsing the html files which are output by ember-cli. These are guaranteed to have the correct JS files in the correct place. A `<discourse-chunked-script>` will allow us to easily identify which chunks belong to which entrypoint.

In future, as we update more entrypoints to be compiled by Embroider/Webpack, we can easily introduce new wrappers.

lib/ember_cli.rb

@@ -37,19 +37,15 @@ module EmberCli
   def self.script_chunks
     return @@chunk_infos if defined?(@@chunk_infos)
 
-    raw_chunk_infos =
-      JSON.parse(
-        File.read("#{Rails.configuration.root}/app/assets/javascripts/discourse/dist/chunks.json"),
-      )
+    chunk_infos = {}
 
-    chunk_infos =
-      raw_chunk_infos["scripts"]
-        .map do |info|
-          logical_name = info["afterFile"][%r{\Aassets/(.*)\.js\z}, 1]
-          chunks = info["scriptChunks"].map { |filename| filename[%r{\Aassets/(.*)\.js\z}, 1] }
-          [logical_name, chunks]
-        end
-        .to_h
+    begin
+      chunk_infos.merge! parse_chunks_from_html("tests/index.html")
+    rescue Errno::ENOENT
+      # production build
+    end
+
+    chunk_infos.merge! parse_chunks_from_html("index.html")
 
     @@chunk_infos = chunk_infos if Rails.env.production?
     chunk_infos
@@ -78,4 +74,22 @@ module EmberCli
         File.basename(full_path)
       end
   end
+
+  def self.parse_chunks_from_html(path)
+    html = File.read("#{Rails.root}/app/assets/javascripts/discourse/dist/#{path}")
+    doc = Nokogiri::HTML5.parse(html)
+
+    chunk_infos = {}
+
+    doc
+      .css("discourse-chunked-script")
+      .each do |discourse_script|
+        entrypoint = discourse_script.attr("entrypoint")
+        chunk_infos[entrypoint] = discourse_script
+          .css("script[src]")
+          .map { |script| script.attr("src")[%r{\A/assets/(.*)\.js\z}, 1] }
+      end
+
+    chunk_infos
+  end
 end