requested to merge jchapman/athena:G4UIManagerUsageFixes_ATLASSIM-3454_21.0 into 21.0
In ATLASSIM-3454 it was noted that many commands added to
simFlags.G4Commands and then executed via the
to have no effect. This was determined to be due to the fact that
they were applied at the wrong point during the Geant4 initialization.
In order to address this, the code has been refactored to try the
commands at multiple points during the initialization until they
succeed. These changes have been checked to make sure that they
don't alter simulation output. They do result in more checks being
switched on the Geant4 than previously so additional
appear in the log. Further iterations may be required.