The new spawn selection algorithm attempts to search the area
around a selected point, in an effort to reduce the total number
of chunk loads required to select a spawn point.
Additionally, the new spawn selection algorithm does not perform
recursion when the selected area is already loaded and owned by
the current region. This fixes https://github.com/PaperMC/Folia/issues/138
Player spawn position changing caused any player to log in while
on a boat to trip a thread check. To resolve this, simply reposition
any mounted entities if they are more than 5 blocks away from the player.
In general, this may happen to other entities that are loaded from
chunks as well. In these cases, we can delete the entity if it itself
is not saved in the correct chunk, and we can reposition the mounted
entities if they are not in the correct chunk. For tile entities,
we can simply remove them if they are not in the chunk.
These changes broadly should make loading player/chunk data more
resiliant to bad logic run by plugins.
Also, the Folia test revealed that the chunk generate rate limiter
also affected chunk loading, which was not intended and has been
resolved by exempting already FULL status chunks from the limit.
