ConfigEntityBase::preSave() doesn't properly support renames; ConfigStorageController::save() preforms renames too early

Updated: Comment #N

Problem/Motivation

ConfigStorageController::save() has this code:

if ($id !== $entity->id()) {
  // Renaming a config object needs to cater for:
  // - Storage controller needs to access the original object.
  // - The object needs to be renamed/copied in ConfigFactory and reloaded.
  // - All instances of the object need to be renamed.
  $config = $this->configFactory->rename($prefix . $id, $prefix . $entity->id());
}

This happens *before* EntityInterface::preSave() is called, which prevents any checks for the existing config, to avoid overwriting it.

However, moving this after the preSave() call breaks ConfigEntityBase::preSave(), which makes false assumptions when checking for existing entities.

This made it impossible to write an alternate entity storage that didn't also move (or delete!) the original entity before this check was run.

Proposed resolution

Move the renaming code in ConfigStorageController after preSave, right before the actual saving.
Fix the logic in ConfigEntityBase::preSave() to allow renames

Remaining tasks

N/A

User interface changes

N/A

API changes

Internal bug fixes, no API changes