[Core][MPI] Reorganize testing utilities

[roigcarlo]

📝 Description
Revised the way cpp tests files and dependencies are compiled both in serial and mpi to solve dependency problems.

Fixes #11548
Implements part of #11506

🆕 Changelog

• Auxiliary files for testing are move outside the cpp test folder.
• Auxiliary files for mpi testing are move outside the mpi/utils folder to a specific location
• Added back test_utility files to the cmake testing target sources.

[loumalouomega]

Looks Okay