Fix bug of GeoJSONWriter when there are sub-objects or sub-array in an array

[kunlinyu]

GeoJSONWriter will throw exception when handle these two cases:

{
  "type": "Feature",
  "geometry": {
    "type": "Point",
    "coordinates": [ 0, 0 ]
  },
  "properties": {
    "matrix": [
      [ 1, 2, 3 ],
      [ 4, 5, 6 ]
    ]
  }
}

{
  "type": "Feature",
  "geometry": {
    "type": "Point",
    "coordinates": [ 0, 0 ]
  },
  "properties": {
    "array": [
      { "key": "value_1" },
      { "key": "value_2" }
    ]
  }
}

the message of the exception is :

cannot use operator[] with a string argument with array

The root cause is here:
https://github.com/libgeos/geos/blob/3.13.0/src/io/GeoJSONWriter.cpp#L112
https://github.com/libgeos/geos/blob/3.13.0/src/io/GeoJSONWriter.cpp#L118

All other scalar types will detect the parent node is object or array.
If the parent is object then use key to add child value, else use push_back.
But when it comes to value.is_array() and value.is_object(), we forget to detect the type of parent json node.

So I add two unit tests to trigger the bug and fix it.