Add brute force approach to GeoHashGridTiler

[iverase]

Currently we always resolve the tiler using recursion which is not optimal when a geometry only touches a few hashes. This PR adds the logic to use brute force approach when it is appropriate very much the shame way we do it in GeoTileGridTiler.

Quick check shows that an aggregation that was timing out (>30s) now takes 4 seconds.

[elasticsearchmachine]

Pinging @elastic/es-analytics-geo (Team:Analytics)

[elasticsearchmachine]

Hi @iverase, I've created a changelog YAML for you.

[craigtaverner]

Looks like a good improvement. The algorithm was a little tricky to follow with the x-increment happening in-line in the loop, but the y-increment hidden inside moveDown which doubled as an initializer. But I got it in the end.