Duplicate seed removal

• Add duplicate seed removal using TrackFindingTool::DuplicateSeedDetector.
  • Duplicate seeds are those where all measurements were already located in a previously followed trajectory.
  • Currently removes duplicates separately for pixels and strips (local to findTracks()), so won't remove duplicate seeds between pixels and strips.
  • We may eventually want to move this functionality to Acts Core, but good test to try it out here.
• Start findTracks() for pixel seeds (previously started with strip seeds).
  • This is probably best until the CKF can do a backward search to find pixel hits from strip seeds.
    • Afterwards, we could start with strips where the occupancy is lower.
    • Actually only relevant when we can remove pixel/strip duplicates.
• TrackStatePrinter prints measurement indices for seeds (instead of stats) and track states (instead of surface names).
• TrackFindingAlg's inputs now optional, allowing to eg. switch off strips seeds.
• Fix broken ATLASSourceLinkGeneric::operator==().