Add a spatial function to convert WKT to Geo-JSON

[Andy2003]

This PR adds a new spatial function spatial.convert.wktToGeoJson to convert WKT to Geo-JSON.

return spatial.convert.wktToGeoJson("MULTIPOLYGON(((15.3 60.2, 15.3 60.4, 15.7 60.4, 15.7 60.2, 15.3 60.2)))") as json

returns an object like

{
  "type": "MultiPolygon",
   "coordinates", [[[
      [15.3, 60.2],
      [15.3, 60.4],
      [15.7, 60.4],
      [15.7, 60.2],
      [15.3, 60.2]
]]]

[craigtaverner]

This seems like a useful function. But it also feels incomplete, missing a few geometry types, and with only one test for one type. I think we need both:

• Unit test for the GeoJsonUtils class that tests all types
• More spatial functions tests for at least a geometrycollection with various types

This is also an opportunity to make a function spatial.asGeoJson that takes a geometry, or a node, and produces GeoJSON. That does not need to be in the PR, but seems like most of the work is already done for that since your implementation makes an intermediate Geometry.