Engine uses Synced terminology for different things

I believe there is some mixed terminology here, that might create some confusion at times, so noting it here for now.

- Synced/deterministic/unsynced as in you will desync from the game if you do something like thread this code.
- Synced/unsynced/asynchronous as in things that happen immediately or get deferred.
- Synced/unsynced as in LOS matters since otherwise you will leak information

Not sure what to do with this, but would be great to have different terminology for the different concepts, there might even be more nuances.

These concepts have some overlap, but they're also separate things.

The issue does not name files, tests, or entry points. First locate the engine's uses of Synced, unsynced, deterministic, asynchronous, and line-of-sight terminology, then clarify the distinct concepts with maintainers; done means each concept has unambiguous terminology documented and applied consistently.

Written by the indexing model from the issue text.