DEV: Improve colocated component rootName logic (#18708)

The complex regex-based detection was based on Ember CLI's implementation, which is necessarily generic and needs to auto-detect the name. In our case, we know the name of the plugin so we can just pass it in - no need for dynamic detection. This resolves issues when there are other files in the `discourse/plugins/{name}` directory which are sorted before `discourse/`

app/assets/javascripts/discourse-plugins/index.js

@@ -171,7 +171,7 @@ module.exports = {
 
     tree = RawHandlebarsCompiler(tree);
 
-    tree = new DiscoursePluginColocatedTemplateProcessor(tree);
+    tree = new DiscoursePluginColocatedTemplateProcessor(tree, pluginName);
     tree = this.compileTemplates(tree);
 
     tree = this.processedAddonJsFiles(tree);