use kind_name as element tag in the xyz file

[superstar54]

The structure.get_ase() method currently outputs an uncontrollable element tag. For instance, if there is a StructureData with a kind having name = X and element = Pt, the resulting aiida.coord.xyz file labels this as Pt1 for the X kind, which can be confusing for users.

This pull request modifies the behavior to use kind_name as the element tag in the XYZ file, enhancing clarity and user experience.