content, directory loaders: Store validated nar as extids
After validating the nar integrity checksums provided by the lister, this now also stores those as ExtID entries (as much as there are checksum hashes provided at initialization time).
This behavior is shared by both Content and Directory loaders. This also only occurs
when the checksums_computation
constructor parameter is set to "nar".
Refs. swh/meta#4979 (closed)
Edited by Antoine R. Dumont