Entity.SourceData and SourceId, provide way to efficiently search by EntityData name

[JaThePlayer]

Second take on the TypeHelper PR, considering the previous one is dead.

• Added Entity.SourceData, Entity.SourceId
• Added Scene.FindEntitiesWithSid(string sid), which filters by entity data name, while still using the tracker.
• Added Tracker.Get[Entities/Components]TrackIfNeeded, which add the type to the tracker if needed, used by the FindEntitiesWithSid method, but is useful in general.
• Added a new Celste.Mod.Registry.EntityRegistry static class, with functions allowing for checking relations between c# types and EntityData names.
  These relations are generated as follows:
  • Vanilla entities are hardcoded
  • [CustomEntity] pointing to a ctor get registered automatically on mod load.
  • Dynamically as they occur, which guarantees they work even with the legacy Everest.Events.Level.LoadEntity event. This does mean that the sets returned by them are not guaranteed to be exhaustive - there could be relations that haven't occurred this session. However, that is fine realistically, because the main point of these APIs is to use them together with the tracker, in which case you don't care about searching for entity types that have never been instantiated anyway.
• It seems like the PR which added Tracker.Refresh/AddTypeToTracker wasn't properly tested? In my testing, the function never did anything, and forcing a refresh caused a missing dictionary key crash for triggers. This PR fixes those bugs as well because these functions are crucial for FindEntitiesWithSid

[JaThePlayer]

Tracker bugfix got moved to #883, which should be merged before this PR