Add Placement Finalizers to Entity/Trigger Handlers

[Cruor]

This PR could have been a issue.

Rejecting it for the following reasons.

• Code style does not match Lönn (as advertised on Discord)
• Naming of the callback function is inconsistent with other handler callbacks
• The implementation doesn't use a "boilerplate" handler function
• The implementation doesn't use the proper helper functions provided for handler callbacks (callIfFunction/isCallable)
• The branch could have been rebased before making the PR
• The PR targets the wrong branch

Besides this, I'm not sure what "my specs" are as you referencing to on discord, this is not the way I would have wanted it implemented.