Use hidden classes for event executors (#11848)

Static final MethodHandles perform similar to direct calls. Additionally,
hidden classes simplify logic around ClassLoaders as they can be defined
weakly coupled to their defining class loader. All variants of methods
(static, private, non-void) can be covered by this mechanism.

paper-server/src/main/java/org/bukkit/craftbukkit/entity/CraftHumanEntity.java

@@ -834,7 +834,7 @@ public class CraftHumanEntity extends CraftLivingEntity implements HumanEntity {
 
     @Override
     @Nullable
-    public Item dropItem(final @Nullable ItemStack itemStack, final boolean throwRandomly, final @Nullable Consumer<Item> entityOperation) {
+    public Item dropItem(final ItemStack itemStack, final boolean throwRandomly, final @Nullable Consumer<Item> entityOperation) {
         // This method implementation differs from the previous dropItem implementations, as it does not source
         // its itemstack from the players inventory. As such, we cannot reuse #internalDropItemFromInventory.
         Preconditions.checkArgument(itemStack != null, "Cannot drop a null itemstack");