Translate "Add {EntityType}" option labels in InlineEntityFormComplex

Problem/Motivation

Bundle labels in the "Add new" dropdown were not being translated. The getBundleInfo() method returns plain string labels that bypass Drupal's translation system, resulting in UI text appearing only in the site's default language regardless of the current language context.

Steps to reproduce

1. Install a Drupal site with multiple languages enabled
2. Create a content type with config translation for the label, @see https://camoa.github.io/dev-guides/drupal/multilingual/config-translation/
3. Add an Inline Entity Form Complex on the type from 2.
4. Switch to a non-default language whilst using the form from 3.
5. Observe: Bundle labels in the "Add new" dropdown remain untranslated (shown in default language)

Proposed resolution

Wrap $bundle_info['label'] with $this->t() to make bundle labels translatable:
$bundles[$bundle_name] = $this->t((string) $bundle_info['label']);
This ensures bundle labels are processed through Drupal's translation system, making them language-aware.

Remaining tasks

None. This is a complete fix.

User interface changes

Bundle labels in the "Add new" entity dropdown will now display in the current site language instead of always showing the default language.

API changes

None.

Data model changes

None.