Get _ignored_source from stored_fields request

Author: jordan-powers

server/src/main/java/org/elasticsearch/search/fetch/PreloadedFieldLookupProvider.java

@@ -47,6 +47,16 @@ public void populateFieldLookup(FieldLookup fieldLookup, int doc) throws IOExcep
             fieldLookup.setValues(Collections.singletonList(id));
             return;
         }
+        if (field.equals(IgnoredSourceFieldMapper.NAME)) {
+            fieldLookup.setValues(
+                preloadedStoredFieldValues.entrySet()
+                    .stream()
+                    .filter(entry -> entry.getKey().startsWith(IgnoredSourceFieldMapper.NAME))
+                    .flatMap(entry -> entry.getValue().stream())
+                    .toList()
+            );
+            return;
+        }
         if (preloadedStoredFieldNames.get().contains(field)) {
             fieldLookup.setValues(preloadedStoredFieldValues.get(field));
             return;