Draft: xAOD::Truth minimal migration
Based on !67195. Requires !76120 (merged).
This merge request implements the minimal barcode to uniqueID migration for xAOD::Truth.
- EDM classes are migrated.
- Helper function calls are updated from HepMC::barcode to HepMC::uniqueID.
- other C++ variable names containing barcode are left unchanged.
- Decoration and TBranch names containing barcode are left unchanged.