Fix Cloner to properly clone ruby strings

Currently, any invocation of clone, including pipeline->pipeline comms and the clone filter
won't actually clone the string data, just the structure. We may be missing other value types too.

This is a start however.

Fixes elastic#9652

Fixes elastic#9653

logstash-core/src/main/java/org/logstash/Cloner.java

@@ -1,5 +1,7 @@
 package org.logstash;
 
+import org.jruby.RubyString;
+
 import java.util.ArrayList;
 import java.util.Collection;
 import java.util.HashMap;
@@ -19,6 +21,8 @@ public static <T> T deep(final T input) {
             return (T) deepMap((Map<?, ?>) input);
         } else if (input instanceof List<?>) {
             return (T) deepList((List<?>) input);
+        } else if (input instanceof RubyString) {
+            return (T) ((RubyString) input).doClone();
         } else if (input instanceof Collection<?>) {
             throw new ClassCastException("unexpected Collection type " + input.getClass());
         }

logstash-core/src/test/java/org/logstash/ClonerTest.java

@@ -0,0 +1,26 @@
+package org.logstash;
+
+import org.jruby.RubyString;
+import org.junit.Test;
+
+import static org.junit.Assert.*;
+
+public class ClonerTest {
+    @Test
+    public void testRubyStringCloning() {
+        String javaString = "fooBar";
+        RubyString original = RubyString.newString(RubyUtil.RUBY, javaString);
+
+        RubyString result = Cloner.deep(original);
+        // Check object identity
+        assertTrue(result != original);
+
+        // Check different underlying bytes
+        assertTrue(result.getByteList() != original.getByteList());
+
+        // Check string equality
+        assertEquals(result, original);
+
+        assertEquals(javaString, result.asJavaString());
+    }
+}