Use originator as the "author" in SpdxDocumentFiles

[sschuberth]

I gave this some though again after the last dev meeting. To me, we should:

• Use originator as the "author", and make use of the existing new mechanism to deduce copyright holders from authors.
• In the future, treat copyrightText as yet another new potential source of copyright holder information in the context of solving Find a generic way to deal with copyright findings than stem from other sources than scanners #3780.

Originally posted by @sschuberth in #3665 (comment)

[sschuberth]

BTW, articles like this one state

In the world of copyright law, the creator of a work [...] is referred to as the author or originator.

So "originator" and "author" are treated synonymously, encouraging me to indeed use SPDX' originator as the author.