Fix standalone DecorHandles

Tadej Novakrequested to merge
tadej/athena:asg/decorhandles into master

This is a standalone version of !38435 (merged). I tried to sync the code and my initial tests confirm DecorHandles now work in AnalysisBase. Part of ATEAM-671.

/cc @ssnyder @krumnack

Edited by Tadej Novak

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