Readd chunk priority patch, including many chunk system fixes from tuinity (#6488)

patches/server/0456-Fix-missing-chunks-due-to-integer-overflow.patch

@@ -0,0 +1,27 @@
+From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
+From: David Slovikosky <davidslovikosky@gmail.com>
+Date: Tue, 9 Jun 2020 00:10:03 -0700
+Subject: [PATCH] Fix missing chunks due to integer overflow
+
+This patch fixes a bug in the WorldChunkManagerTheEnd class where the distance
+from 0,0 squared overflows the maximum size of an integer. The overflow leads
+to hard chunk borders around 370,000 blocks from 0,0. After this cutoff there
+is a few hundred thousand block gap before end land resuming to generate at
+530,000 blocks from spawn. This is due to the integer flipping back and forth.
+
+The fix for the issue is quite simple, casting chunk coordinates to longs
+allows the distance calculation to avoid overflow and work as intended.
+
+diff --git a/src/main/java/net/minecraft/world/level/biome/TheEndBiomeSource.java b/src/main/java/net/minecraft/world/level/biome/TheEndBiomeSource.java
+index 7f7b0c961a76119b6004da03fe01ff4e2ae41628..9a64ab092ac8616ed8b9ea5c1e8677dda5c4333c 100644
+--- a/src/main/java/net/minecraft/world/level/biome/TheEndBiomeSource.java
++++ b/src/main/java/net/minecraft/world/level/biome/TheEndBiomeSource.java
+@@ -84,7 +84,7 @@ public class TheEndBiomeSource extends BiomeSource {
+         int l = j / 2;
+         int m = i % 2;
+         int n = j % 2;
+-        float f = 100.0F - Mth.sqrt((float)(i * i + j * j)) * 8.0F;
++        float f = 100.0F - Mth.sqrt((long) i * (long) i + (long) j * (long) j) * 8.0F; // Paper - cast ints to long to avoid integer overflow
+         f = Mth.clamp(f, -100.0F, 80.0F);
+ 
+         for(int o = -12; o <= 12; ++o) {