ExternalSourceAspects created by "in iModel" transformation or PlantSight Aggregation not usable after branch/merge

[PaulPierog]

Describe the bug
ExternalSourceAspects used to track provenance for "in iModel" transformations and PlantSight Aggregation assign ElementIds to the ExternalSourceAspect.identifier property and ExternalSourceAspect.jsonProperties fields. These ElementIds are not updated correctly after executing a branch/merge operation.

To Reproduce
Steps to reproduce the behavior, (shell scripts appreciated):
An ATP has been created to repeat the error. Link to PR:
#48

Expected behavior
The ElementIds stored in the ExternalSourceAspects should be updated to reflect the ElementId changes that happened during a merge operation.

Desktop (please complete the applicable information):

• OS: Windows 10
• @itwin/imodel-transformer Version 0.1.8
• iTwin.js Version 3.7.1

Additional context