Facet functions emit date fields as ticks

When invoking a facet function in the JSON Facet API, TrieDateField is coerced into a numeric value and the result of the function is emitted as numeric instead of being converted back into a formatted date.

Example:

curl http://localhost:8983/solr/query?q=*:*&json.facet=

Produces (in part):

"facets":{
"count":38304,
"most_recent":1.489012400831E12}}

The "most_recent" attribute would be more useful if it was converted back to an iso8601 formatted date.

There was a thread discussing this issue in 2016: http://lucene.472066.n3.nabble.com/min-max-on-date-fields-using-JSON-facets-td4288736.html#a4288781