LUCENE-5666: move sortedset sortfield out of sandbox

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/branches/lucene5666@1594204 13f79535-47bb-0310-9956-ffa450edef68
LUCENE-5666: add SortedSetFieldSource

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/branches/lucene5666@1594211 13f79535-47bb-0310-9956-ffa450edef68