SPIGOT-1806: Add HumanEntity#getMainHand

By: Matthew <stteg@hotmail.com>

paper-api/src/main/java/org/bukkit/entity/HumanEntity.java

@@ -2,6 +2,7 @@ package org.bukkit.entity;
 
 import org.bukkit.GameMode;
 import org.bukkit.Location;
+import org.bukkit.inventory.MainHand;
 import org.bukkit.inventory.Inventory;
 import org.bukkit.inventory.InventoryHolder;
 import org.bukkit.inventory.InventoryView;
@@ -36,6 +37,13 @@ public interface HumanEntity extends LivingEntity, AnimalTamer, Permissible, Inv
      */
     public Inventory getEnderChest();
 
+    /**
+     * Gets the players selected main hand
+     *
+     * @return the players main hand
+     */
+    public MainHand getMainHand();
+
     /**
      * If the player currently has an inventory window open, this method will
      * set a property of that window, such as the state of a progress bar.

paper-api/src/main/java/org/bukkit/inventory/MainHand.java

@@ -0,0 +1,9 @@
+package org.bukkit.inventory;
+
+/**
+ * Represents the chosen main hand of a player
+ */
+public enum MainHand {
+    LEFT,
+    RIGHT
+}