Convert static PutDraftComment#side(Comment) method to method on Comment

Change-Id: I9c3956257f1187150d62a228d2ab91515960174d
Signed-off-by: Edwin Kempin <ekempin@google.com>

gerrit-extension-api/src/main/java/com/google/gerrit/extensions/client/Comment.java

@@ -59,6 +59,13 @@ public abstract class Comment {
     }
   }
 
+  public short side() {
+    if (side == Side.PARENT) {
+      return (short) (parent == null ? 0 : -parent.shortValue());
+    }
+    return 1;
+  }
+
   @Override
   public boolean equals(Object o) {
     if (this == o) {