Make fake players compatible with adventure platform lib and minor refactor around them (#1235)

* Make fake players compatible with adventure platform and minor refactor around them

Cleaner approach

* Remove no longer needed enderpearl mixin for fake players

Their ClientConnection now has an open channel so isOpen returns true

src/main/java/carpet/fakes/ClientConnectionInterface.java

@@ -0,0 +1,7 @@
+package carpet.fakes;
+
+import io.netty.channel.Channel;
+
+public interface ClientConnectionInterface {
+    void setChannel(Channel channel);
+}