Issue #2957425 by tedbow, johndevman, mpotter, tim.plunkett, hawkeye.twolf,...

Issue #2957425 by tedbow, johndevman, mpotter, tim.plunkett, hawkeye.twolf, alexpott, Berdir, samuel.mortenson, xjm, kevincrafts, jibran, amateescu, larowlan, twfahey, EclipseGc, sjerdo, japerry, mtodor, phenaproxima, johnzzon, mglaman: Allow the inline creation of non-reusable Custom Blocks in the layout builder

(cherry picked from commit 4ed41f4e)