The code used to rely on the dimension. However, the dimension can only
be read from a GML3 document. This caused, for 3D geometries:
- An assertion error to be raised since the flatCoordinates list
contains more than 3 elements: "Assertion failed: flatCoordinates should
have a length of 3" The value of flatCoordinates for a 3D point was
something like `[2586394, 1232407, 0, 731, NaN, 0]`
- The value of the Z coordinates to be incorrect and always set to 0
This patch simplifies and correct the parsing of the coordinates:
- Don't parse groups of coords and the coordonates at the same time.
- Detect the dimension for the coordinates.
- If the Z coordinate exists, its value is used, otherwise, we use 0.
- Correct the presentation of test data to make it work with the new
parser.
- Add a test for a 3D point.
