1.15.2 update (#2887)

Functional GUI fix added by billygalbreath

Spigot-API-Patches/Remove-deadlock-risk-in-firing-async-events.patch

@@ -16,7 +16,7 @@ which results in a hard crash.
 This change removes the synchronize and adds some protection around enable/disable
 
 diff --git a/src/main/java/org/bukkit/entity/Entity.java b/src/main/java/org/bukkit/entity/Entity.java
-index adca48f1..2d3cee14 100644
+index 79b94800..04365232 100644
 --- a/src/main/java/org/bukkit/entity/Entity.java
 +++ b/src/main/java/org/bukkit/entity/Entity.java
 @@ -0,0 +0,0 @@ import org.jetbrains.annotations.Nullable;