Changes

Paper-only event `player tracks|untracks <entity>` (#2444)

* Add paper-only event `player tracks|untracks <entity>`

* Explain when an entity is tracked or untracked.

* Meta + code improvements

Thanks Mergu, Aya, Icecapade, and Wahrheit!

* Remove `<context.location>` and change order of `runInCheck`

Thanks Mergu for the suggestions!

* Change event handler names
 (commit: 7b382dc)