Some minor JS cleanup (#2846)

- Change index files to ts
- Remove deprecated EditUserModal from forum compat
- Remove b14-specific error
- Remove transChoice method (ICU should be used instead)
- Translator to TypeScript
- Small JS => TS cleanup
* Trivial js => ts change

Co-authored-by: David Wheatley <hi@davwheat.dev>

js/src/forum/compat.js

@@ -69,10 +69,6 @@ import Search from './components/Search';
 import DiscussionListItem from './components/DiscussionListItem';
 import LoadingPost from './components/LoadingPost';
 import PostsUserPage from './components/PostsUserPage';
-/**
- * @deprecated
- */
-import EditUserModal from '../common/components/EditUserModal';
 import DiscussionPageResolver from './resolvers/DiscussionPageResolver';
 import BasicEditorDriver from '../common/utils/BasicEditorDriver';
 import routes from './routes';
@@ -131,10 +127,6 @@ export default Object.assign(compat, {
   'components/EventPost': EventPost,
   'components/DiscussionHero': DiscussionHero,
   'components/PostMeta': PostMeta,
-  /**
-   * @deprecated Used for backwards compatibility now that the EditUserModal has moved to common. Remove in beta 17.
-   */
-  'components/EditUserModal': EditUserModal,
   'components/SearchSource': SearchSource,
   'components/DiscussionRenamedPost': DiscussionRenamedPost,
   'components/DiscussionComposer': DiscussionComposer,