Rename all references of swh PIDs to SWHIDs for consistency
When Software Heritage persistent identifiers were introduced, they were not yet abbreviated as SWHIDs.
Now that abbreviation is growing adoption, rename old persistent identifiers refererences in function names, variables names, comments and documentation for consistency.
It's been a while since I wanted to do that renaming. I did it in one pass so the diff is huge but basically this is just renaming some stuffs.
Migrated from D3419 (view on Phabricator)