Replace dfmt.polyline_mapslice with uds.intersect_line

[veenstrajelmer]

replace dfmt.polyline_mapslice() with new uds.intersect_line and uds.intersect_linestring implemented in Deltares/xugrid#155

In get_xzcoords_onintersection the variable uds_sel can be derived with:

from shapely import LineString
uds_sel = uds.ugrid.intersect_linestring(LineString(line_array))
uds_sel = uds_sel.rename_dims(nmesh2d_face='ncrossed_faces')

This contains also mesh2d_s (distance from start of line). However this is in degrees in case of geographic data. Also, it does not contain the coordinates of the intersections between edges and linestring (they are reduced here), but only the centers instead. It does seem to contain sorting, which is good.