Special handling of "BSD" license declaration

right now `SPDX.normalize("BSD") === "NOASSERTION"`

Looking through a lot of the causes for NOASSERTION, BSD has popped up a lot.
Instead of declaring this as junk, we can consider treating "BSD" as no information and letting our other indicators take precendence.

For example, if you pack a BSD-3-Clause license file, but declare your package as "BSD" in your manifest, we could fall back to the license detection on the license file