FIX: Use <textarea> for theme translations (#14322)

Translations are often multi-line. Using a regular `<input>` doesn't allow newlines, so if you try to edit a multiline theme translation, all the line breaks will be removed.

This commit updates the theme translations UI to use `<textarea>`, just like the core translation editing UI.

app/assets/javascripts/admin/addon/controllers/admin-customize-themes-show.js

@@ -146,7 +146,9 @@ export default Controller.extend({
 
   @discourseComputed("model.translations")
   translations(translations) {
-    return translations.map((setting) => ThemeSettings.create(setting));
+    return translations.map((setting) =>
+      ThemeSettings.create({ ...setting, textarea: true })
+    );
   },
 
   hasTranslations: notEmpty("translations"),