HLTEDMCreatorAlg: split view merging and gap filling config

Split the view merger and gap filler configuration into separate Cfg functions. This is in preparation for running the gap filler at Tier-0.

Changes to configuration in test_trigP1_v1PhysP1_noL1Sim_dumpConfig_build.py:

Component EDMCreatorAlg.ViewsMergingTool may differ
        LateEDMKeys =  ['HLTNav_Summary_OnlineSlimmed', 'HLT_RuntimeMetadata']  vs  []   <<

which is OK because the view merger does not look at these collection anyway.

Relates to ATR-27986.

cc @tamartin @tbold