Restore import that was removed during a backport but still needed in this branch

Author: jimczi

core/src/main/java/org/elasticsearch/index/mapper/AllFieldMapper.java

@@ -19,6 +19,7 @@
 
 package org.elasticsearch.index.mapper;
 
+import org.apache.lucene.document.Field;
 import org.apache.lucene.index.IndexOptions;
 import org.apache.lucene.index.Term;
 import org.apache.lucene.search.Query;