Filter for locations in a geofence

[elffjs]

Add in two new filters for values being fed into aggregations of Location-valued fields:

inPolygon: [{latitude: 37.32, longitude: 122.02}, …]

and

inCircle: {center: {latitude: 37.32, longitude: 122.02}, radius: 700}

Loose ends:

• I do not expect good results from the polygon filter for locations near the edges of the coordinate system.
• I have not tested out what happens when a polygon is not properly oriented, or if it has self-intersections.
• Need to add HDOP filtering. Maybe a separate PR.

[linear]

PR-3897 Filter locations in geofence