Issue #3042745 by dwebpoint, Berdir, emacoti, jefftrnr, Wim Leers, alexpott, voleger, sjhuda, bnjmnm: Remove group @legacy from jsonapi tests and fix deprecation messages

Issue #2972445 by sudheeshps, sjhuda, andrewmacpherson, alexpott: Docblock for dropbutton theme function is incorrect