Issue #3347291 by lauriii, srishtiiee, tim.plunkett, hooroomoo, narendraR, tedbow, bnjmnm, alexpott, Berdir: Combine field storage and field instance forms

Issue #2537732 by Xano, tim.plunkett, gnuget, claudiu.cristea, drunken monkey, bojanz: PluginFormInterface must have access to the complete $form_state (introduce SubFormState for embedded forms)