xAODTruthCnv Improvement, main branch (2025.09.16.)

After some follow up, it turned out that !82613 (merged) doesn't work as well in Athena as I hoped. ☹️

@ssnyder explained that in our current setup the truth particle containers that we have in the DAOD files would continue pointing at the original containers with their links. (It's a bit of a longer story, see: https://egroups-archives.web.cern.ch/group/atlas-sw-core/thread/eyJ0aHJlYWRfdG9waWMiOiAiQUFRa0FHVm1PVGt5TlRWa0xUUTNPVEV0TkdFMFl5MDVNR1F6TFRBMU1qVTJNek5qTnpZME1nQVFBTWZTdEFfYTFrOUJtaHo5a0RrakRLRT0ifQ==)

I hoped that I could put a work around in place in a quite generic way, but in the end I had to decide that going low-tech was the way to go after all. So I just extended the algorithms introduced in !82613 (merged) to also massage a set of element links on the fixed containers.

@ravinab and @tstreble, this is not quite the "elegant solution" that I had in mind during the morning. ☹️ But hopefully it will be good enough. 🤔 I think you should be able to use the new capabilities of the algorithms to make your analysis setups work finally. Though I only did some very simple runtime tests with the code. You guys will need to test these changes more carefully.