Allow to search for ignored changes by "is:ignored"

Searching by "is:ignored" is the same as "star:ignore" but is a bit
more intuitive for users.

Change-Id: I63f41662ad1023c98fa746a892d5bfa050303879

gerrit-server/src/main/java/com/google/gerrit/server/query/change/ChangeQueryBuilder.java

@@ -598,6 +598,10 @@ public class ChangeQueryBuilder extends QueryBuilder<ChangeData> {
       return new SubmittablePredicate(SubmitRecord.Status.OK);
     }
 
+    if ("ignored".equalsIgnoreCase(value)) {
+      return star("ignore");
+    }
+
     try {
       return status(value);
     } catch (IllegalArgumentException e) {