libbluetooth: Move to the bluetooth-lib package

Move the library, but not any of the runtime. This allows executables
to link against libbluetooth without having to pull in the entire BT
stack.

MFC after: 3 days
Reviewed by: dch, emaste
Sponsored by: https://www.patreon.com/bsdivy
Differential Revision: https://reviews.freebsd.org/D53016

(cherry picked from commit 426891e0f8f1cfae0263ba81ea55f46c547d7762)