Feature: API to switch items in the offhand/mainhand (#4819)

Author: onebeastchris

api/src/main/java/org/geysermc/geyser/api/entity/EntityData.java

@@ -81,4 +81,10 @@ public interface EntityData {
      * @return whether the movement is locked
      */
     boolean isMovementLocked();
+
+    /**
+     * Sends a request to the Java server to switch the items in the main and offhand.
+     * There is no guarantee of the server accepting the request.
+     */
+    void switchHands();
 }

core/src/main/java/org/geysermc/geyser/entity/GeyserEntityData.java

@@ -96,4 +96,9 @@ public boolean lockMovement(boolean lock, @NonNull UUID owner) {
     public boolean isMovementLocked() {
         return !movementLockOwners.isEmpty();
     }
+
+    @Override
+    public void switchHands() {
+        session.requestOffhandSwap();
+    }
 }