MC-137353: Don't go crazy on amount of bootstrap threads needed

nms-patches/DataConverterRegistry.patch

@@ -1,6 +1,20 @@
 --- a/net/minecraft/server/DataConverterRegistry.java
 +++ b/net/minecraft/server/DataConverterRegistry.java
-@@ -185,6 +185,18 @@
+@@ -21,7 +21,12 @@
+         DataFixerBuilder datafixerbuilder = new DataFixerBuilder(1631);
+ 
+         a(datafixerbuilder);
+-        return datafixerbuilder.build(ForkJoinPool.commonPool());
++        // CraftBukkit start
++        ForkJoinPool pool = new ForkJoinPool(Integer.getInteger("net.minecraft.server.DataConverterRegistry.bootstrapThreads", Math.min(Runtime.getRuntime().availableProcessors(), 2)));
++        DataFixer fixer = datafixerbuilder.build(pool);
++        pool.shutdown();
++        return fixer;
++        // CraftBukkit end
+     }
+ 
+     public static DataFixer a() {
+@@ -185,6 +190,18 @@
          datafixerbuilder.addFixer(new DataConverterItemFrame(schema46, false));
          Schema schema47 = datafixerbuilder.addSchema(1458, DataConverterRegistry.b);