Add per player chunk loading limits

Configurable under "settings.chunk-loading.player-max-chunk-load-rate",
defaults to -1. This commit also changes the chunk loading to be
distributed equally for all players, rather than distance based. This is
to ensure players flying around do not take priority over everyone else.
The exception to this new rule is the min-load-radius, which still has
priority over everything else.

patches/server/Option-to-have-default-CustomSpawners-in-custom-worl.patch

@@ -14,8 +14,8 @@ index 0000000000000000000000000000000000000000..00000000000000000000000000000000
 --- a/src/main/java/com/destroystokyo/paper/PaperConfig.java
 +++ b/src/main/java/com/destroystokyo/paper/PaperConfig.java
 @@ -0,0 +0,0 @@ public class PaperConfig {
-         }
          globalMaxConcurrentChunkLoads = getDouble("settings.chunk-loading.global-max-concurrent-loads", 500.0);
+         playerMaxChunkLoadRate = getDouble("settings.chunk-loading.player-max-chunk-load-rate", -1.0);
      }
 +
 +    public static boolean useDimensionTypeForCustomSpawners;