temporary workaround for xAOD dictionary issues in AnalysisBase

This is meant to be just a temporary workaround, as currently there are issues with loading the xAOD dictionaries in AnalysisBase that can be very hard for users to debug and understand. And particularly since a more permanent fix is currently under development it seemed easiest to import the corresponding workaround from 21.2 for the time being instead of integrating all the workarounds into each of the current unit tests and then taking them out again in a few weeks.

This is mostly the same code as in LoadDictionaries() in 21.2, but I replaced the use of a preprocessor macro with a simple for loop, and slightly adjusted the messaging to match the rest of the function.

Running all unit tests, since this code gets run in essentially all tests within AnalysisBase.

cc @akraszna