Implemented a way to close forms from floodgate (#5247)

* feat: send close form packet when receiving empty form data

* use session#closeForm

---------

Co-authored-by: Roch Blonndiaux <contact@roch-blondiaux.com>
Co-authored-by: onebeastchris <github@onechris.mozmail.com>

core/src/main/java/org/geysermc/geyser/translator/protocol/java/JavaCustomPayloadTranslator.java

@@ -67,6 +67,12 @@ public void translate(GeyserSession session, ClientboundCustomPayloadPacket pack
             session.ensureInEventLoop(() -> {
                 byte[] data = packet.getData();
 
+                // If the data is empty, we just need to close the form
+                if (data.length == 0) {
+                    session.closeForm();
+                    return;
+                }
+
                 // receive: first byte is form type, second and third are the id, remaining is the form data
                 // respond: first and second byte id, remaining is form response data
 
@@ -96,7 +102,6 @@ public void translate(GeyserSession session, ClientboundCustomPayloadPacket pack
                 });
                 session.sendForm(form);
             });
-
         } else if (channel.equals(PluginMessageChannels.TRANSFER)) {
             session.ensureInEventLoop(() -> {
                 byte[] data = packet.getData();