Add new class ExtendedSWHID as an alternative to SWHID/QualifiedSWHID

Following the discussion on T3034, we decided to replace SWHID with
two or three classes:

* QualifiedSWHID to replace the existing SWHID (standard types + qualifiers)
* CoreSWHID, for "core SWHID" only (standard types + no qualifiers)
* ExtendedSWHID for internal use in Software Heritage (extra types + no qualifiers)

This commit adds the last one.

It also removes "ori" as a valid object type for CoreSWHID and
QualifiedSWHID, as it now only belongs in ExtendedSWHID.