Issue #2959493 by bnjmnm, phenaproxima, tim.plunkett, tedbow, Adrian83, lauriii, xjm, andrewmacpherson, johndevman, KarenS, alwaysworking, jrockowitz, ckrina, cboyden, webchick, seanB, benjifisher, larowlan: Allow Layout Builder live previews to be toggled to allow easier drag-and-drop

(cherry picked from commit d028385c)