[MC-164281] Lighting thread and gameplay thread can desync

The bug

In a previous version the lighting engine was moved to a separate thread. However it appears there is nothing which prevents desync between the gameplay and the lighting thread.

This can cause all kind of unexpected behavior, for example:

Being unable to plant crops in lit up caves
Monters spawning in lit up areas
Stopping the server / closing a world when the lighting thread has not caught up causes pending light updates to get lost

How to reproduce

Place a repeating command block (always active), pointing upwards
```
fill ~ 255 ~ ~20 255 ~20 stone
```
Place a chain command block above (always active)
```
fill ~ 255 ~ ~20 255 ~20 air
```
Set the time to night
```
/time set night
```
Open the debug screen (F3)
Place a light source, e.g. a torch
The "block" value for "Server light" does not change
Reopen the world
The area around the light source is not lit up