sweep of various EventLoop updates from main back into 21.2
The main thing we want here are the grid driver updates, but I figured it is easier/better to sweep everything that has been done so that I don't have to deal with merge conflicts. I left out one or two MRs that relied on code only present in main, and had to disable one newly introduced test for an experimental feature as it was having issues, and remove the new TEfficiency code for AthAnalysis.
Please note: Since this is a sweep aimed at making both branches consistent again, please restrict the review to things that really need to be fixed. Coding improvements ought to go into main and then be swept again.
List of commits swept: