Ensure that various G4 Manager member variables are properly set in Athena implementations of G4UserActions

See explanation from Mihaly Novak on ATLASSIM-6165:

When Geant4 is used from Athena, real G4 user actions of a given type are registered in the G4RunManager (and their interface methods are eventually invoked) through a wrapper G4 user action of that type. Therefore, some fields are set only for the wrapper user action but not for the real wrapped user actions.

As an example, G4UserTrackingAction implementations (such as AthenaTrackingAction) are wrapped in the G4AtlasTrackingAction:

• G4AtlasTrackingAction also derives from G4UserTrackingAction and actually this will be the only one registered in the G4RunMangerand thus invoked during the event processing.
• the real tracking actions (e.g. AthenaTrackingAction) are added to this wrapper (stored in a vector field)
• Whenever the (Pre/PostUserTrackingAction) interface of G4AtlasTrackingAction is invoked by the run manager, it just iterates over all registered real user tracking actions and invokes the corresponding interface method.
• As only the wrapper G4AtlasTrackingAction is registered directly in the G4RunManager, only its fpTrackingManager field is set properly (during registration) while all real user tracking action fpTrakingManager field are unset, i.e. left to be null as initialised.

In addition to the G4UserTrackingAction fix, also set manager properties in the other UserAction types.

No effect on output expected, but improving the initialization robustness will allow other developments discussed in ATLASSIM-6165 to proceed.

Tagging @mnovak, @mbandier, @tlari.