Improve map-polyline-slice dataset structure and cleanliness

[veenstrajelmer]

Very maybe uds.ugrid.sel(x/y) could help out here (Deltares/xugrid#26). Or for instance implement uds.ugrid.isel(faces=idx_faces), where also edges/nodes are subsetted (Deltares/xugrid#32) >> fixed

If it would be possible subset an entire dataset (dims: faces, edges, nodes) based on faceidx, it would also be easier to remove ghostcells as in dfmt.open_partitioned_dataset() (#207)

• replace shapely intersection method with xu.grid.intersect_edges: convert map cross section (polygon slice) to xugrid alternative #252
• cleanup deprecated code (polyline_mapslice and polygon_intersect) #277
• add unittest for intersect_edges_withsorting() #275
• select only face-variables in the process, other variables are not sliced (currently edgedim and nodedim are dropped) #302
• polyline_mapslice() now uses xu.ugrid2d.intersect_edges and sorts them. Put sorting in intersect_edges or numba.celltree (Move snap_to_edges to numba_celltree xugrid#65 is probably related) >> this seems to be solved, but check more thoroughly
• Replace dfmt.polyline_mapslice with uds.intersect_line #682
• calcdist_fromlatlon is derived from hardcoded varnames wgs84 or projected_coordinate_system, maybe Parse CRS if present xugrid#42 (but would still require conversion to cartesian/spherical). At least find coordvar based on attribute if possible.
• improve ugrid generation of sideview grid (maybe with temporal variations), maybe in xugrid? (Investigate a cross section plot xugrid#59 exists)
• hovmoller support, so slice multiple times at once
• Investigate a cross section plot xugrid#59
• Simplify line plots along cross-section #673
• polyline_mapslice fails for mapformat1 #648