SOLR-5875: QueryComponent.mergeIds() unmarshals all docs' sort field values once per doc instead of once per shard. (merged trunk r1578434)

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/branches/branch_4x@1578435 13f79535-47bb-0310-9956-ffa450edef68