Support asynchronous events; Addresses BUKKIT-1212

By: Wesley Wolfe <weswolf@aol.com>

paper-api/src/main/java/org/bukkit/Bukkit.java

@@ -365,4 +365,8 @@ public final class Bukkit {
     public static int getWaterAnimalSpawnLimit() {
         return server.getWaterAnimalSpawnLimit();
     }
+
+    public static boolean isPrimaryThread() {
+        return server.isPrimaryThread();
+    }
 }