[ATR-19253] TriggerFeature access in the MT Trigger

This MR works towards being able to access 'Features' from the new trigger navigation structure.

• This does not re-use much in terms of existing code due to the new navigation structure departing from the old, and how deeply baked the navigation is into the current functions.
• I still hope to re-use combinatoric logic from the current code, if possible.
• TrigComposite ElementLink retrieval is relaxed to allow for features to be returned via base class (I.e. IParticleContainer)
• Functions are added to navigate the decision graph, and return features.
• The way the HLTSummary alg stores its decisions is modified as on https://its.cern.ch/jira/browse/ATR-19551?focusedCommentId=2535137&page=com.atlassian.jira.plugin.system.issuetabpanels%3Acomment-tabpanel#comment-2535137