Conflict doesn't work with Content Moderation

Problem/Motivation

Conflict's pipeline gates on `$entity->isDefaultRevision()` in two places:
`conflict_prepare_entity_form()` and `ContentEntityConflictHandler::entityFormEntityBuilder()

If the entity is under content moderation, "$entity->isDefaultRevision()" returns false, preventing the conflict functionality from continuing, and the Conflict merge UI is never shown.

Steps to reproduce

1. Enable Conflict + Content Moderation; apply editorial workflow to Article.
2. Create an article.
3. Open the edit form in two sessions.
4. Save different changes from each.
Expected: second submitter sees the conflict UI.
Actual: the second save is blocked by default Drupal constraint:
"The content has either been modified by another user, or you have already submitted modifications. As a result, your changes cannot be saved"