Add support for lat / long field types

[uxder]

Description

Latitude and longitude coordinates are commonly used on sites that display maps with markers. Tools like GeoJSON.io or Google Maps provide ways to acquire these coordinates, but the lookup process can be tedious and unintuitive.

Please add support for latitude and longitude fields, ideally with a map selector for ease of use.

[stevenle]

Quick note of other systems with similar field types:

• "Geopoint" https://www.sanity.io/docs/geopoint-type
• "Location" https://www.contentful.com/developers/docs/concepts/data-model/