FCameraShakePreviewer retains world-outered UCameraShakeBase instances indefinitely, fataling CheckForWorldGCLeaks on editor map change

FCameraShakePreviewer is an FGCObject that strongly references the UCameraShakeBase instances it previews, and creates them outered to the previewed UWorld. Nothing releases them on world teardown, so after a Sequencer camera-shake trigger fires, the next editor map change leaves the outgoing world and its package alive and UEditorEngine::CheckForWorldGCLeaks raises a fatal error.

Steps to Reproduce

Run unreal at 5.7.4

1. Open a map in the editor
2. Open a ULevelSequence containing a camera shake trigger track whose shake class has an infinite / looping pattern (i.e. UCameraShakeBase::IsFinished() never returns true).
3. Scrub or play the sequence so the trigger fires at least once. TriggerOneShotShakes adds a preview instance via FCameraShakePreviewer::AddCameraShake.
4. Open a different level (File > Open Level, or any path reaching FEditorFileUtils::LoadMap).
5. Fatal error as above. Setting gc.historysize 1 first makes the retaining chain visible.