Find searches for the name in the export map.
If no matches exist, the name is unique and returned.
Otherwise find attempts to append a `_1` suffix to the
name. If the name already has this suffix, the digit
is incrementally increased until a unique name is returned.
Unique checks the destination path against an export map.
The map contains a unique collection of previously used destination
paths, to avoid creating duplicate text filenames while using the
SaveName config.