Enable recording name_type of link targets

[ajnelson-nist]

A POSIX soft link only records a path without type hints. In cases where the link target is not recorded in the same DFXML stream, it would be helpful to be able to record the type of the target (e.g. whether the soft link is pointing at a directory, file, block device, etc.).

This can be represented with an element link_target_name_type, with its text being the same enumeration as in name_type.

Thanks to @B0bK4t for discussion that lead to this.