[bug] Fix FILES sort and path provider issue

[jimschubert]

The FILES metadata is supplementary, but was logging a warning while
generating Ada client that FILES couldn't be written. An exception was
being thrown because Path was being reported as two different "types of
Path". One would be reported as mac file, while the other was reported
as a unix file. The fix here is to disconnect path details from the
underlying file system provider by creating a new Path based on the
file's absolute path. This change also fixes sorting so it works
alphabetically in ascending order.

cc @OpenAPITools/generator-core-team

fixes #7715

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