DEV: Clean up imports (#28060)

* `@ember/owner` instead of `@ember/application`
* `discourse-i18n` instead of `I18n`
* `{ service } from "@ember/service"` instead of `inject as service`

plugins/chat/test/javascripts/components/chat-thread-list-item-test.js

@@ -1,4 +1,4 @@
-import { getOwner } from "@ember/application";
+import { getOwner } from "@ember/owner";
 import { render } from "@ember/test-helpers";
 import hbs from "htmlbars-inline-precompile";
 import { module, test } from "qunit";