Content Moderation hardcodes the 'edit' and 'default' form modes — other form modes are not supported

Just ran into this codepath with paragraphs_library which ends up with the add operation on the add form (rather than default). This means that quite a few things don't happen in EntityTypeInfo::formAlter(), noteably for my case it was this little bit:

      if (isset($form['footer']) && in_array($form_object->getOperation(), ['edit', 'default'], TRUE)) {
        $form['moderation_state']['#group'] = 'footer';
      }

Which was causing the moderation_state dropdown to be above the revision log field on the add screen but not the edit screen.

This is also inside an elseif which checks isModeratedEntityEditForm - that also checks the form operations but also includes layout_builder.

This bug also causes issues when adding translations that should be moderated.

• Contrib module or custom code adds a node form class for "add".
• Adding a translation: The "\Drupal\content_translation\Controller\ContentTranslationController::add()" uses the following code to to set the form operation to "add".
  

  $operation = $entity->getEntityType()->hasHandlerClass('form', 'add') ? 'add' : 'default';
  

• Entity Prepare Form: \Drupal\content_moderation\EntityTypeInfo::entityPrepareForm() uses EntityTypeInfo::isModeratedEntityEditForm() to alter the form to add a redirect. The "add" form mode is not detected by "isModeratedEntityEditForm".
  
  RESULT: The new revision is not created correctly leaving the entity's "revision_translation_affected" set to TRUE. This causes all sort of revisioning issues such as "revision_translation_affected" set to TRUE for the source translation's revision that is linked to the new language translation.
• Form altering: \Drupal\content_moderation\EntityTypeInfo::formAlter() uses EntityTypeInfo::isModeratedEntityEditForm() to alter the form to add a redirect. RESULT: Redirect to the latest-version is not set since "add" is not listed in "isModeratedEntityEditForm"

Proposed Resolution

Add "add" to the form operation list in \Drupal\content_moderation\EntityTypeInfo::isModeratedEntityEditForm().
This is not ideal but a similar patch has been already added to "isModeratedEntityEditForm()" for "layout_builder".

I've also run into this problem and agree it should be configurable in some way, but open to suggestions on the best way. A `hook_entity_type_info_edit_form_modes_alter` perhaps, or it being defined as part of the form mode. I'm happy to get started on a solution.