Heavily optimise random block ticking (#2914)

* Optimise random block ticking

Massive performance improvement for random block ticking.
The performance increase comes from the fact that the vast
majority of attempted block ticks (~95% in my testing) fail
because the randomly selected block is not tickable.

Now only tickable blocks are targeted, however this means that
the maximum number of block ticks occurs per chunk. However,
not all chunks are going to be targeted. The percent chance
of a chunk being targeted is based on how many tickable blocks
are in the chunk.
This means that while block ticks are spread out less, the
total number of blocks ticked per world tick remains the same.
Therefore, the chance of a random tickable block being ticked
remains the same.

Spigot-Server-Patches/Allow-overriding-the-java-version-check.patch

@@ -6,7 +6,7 @@ Subject: [PATCH] Allow overriding the java version check
 -DPaper.IgnoreJavaVersion=true
 
 diff --git a/src/main/java/org/bukkit/craftbukkit/Main.java b/src/main/java/org/bukkit/craftbukkit/Main.java
-index eb5f44e30..af05f3c1e 100644
+index eb5f44e300..af05f3c1e0 100644
 --- a/src/main/java/org/bukkit/craftbukkit/Main.java
 +++ b/src/main/java/org/bukkit/craftbukkit/Main.java
 @@ -0,0 +0,0 @@ public class Main {