make data handles "functional" in 21.2
This should introduce a sort of limited functionality of the data handles in 21.2, essentially I tried to make sure that everything that worked in the unit test for the stand-alone handles also worked in AthAnalysis. This involved using the stand-alone decoration handles in Athena as well, rather than trying to backport the full decoration handles from master, which would likely run into issues with the rather ancient version of gaudi in 21.2. It also added the inline constructors to the existing data handles for 21.2, to be consistent with the standalone data handles.
This is not meant to work with AthenaMT, it is just meant to make it easier to share code between 21.2 and master. I'm also not trying to guarantee that anything works that is not tested by the unit tests for the dual-use handles. I did add special warnings in several files to make sure that they will not accidentally end up in master.