Issue #2030191 by andypost, j2r, forbesgraham, henk, InternetDevels, IshaDakota, millerbennett: Clean-up api examples of node module

Issue #2093173 by longwave, Cyberschorsch, forbesgraham, sandipmkhairnar, damiankloip, rbayliss, grom358, harijari, InternetDevels, dawehner: Remove all calls to drupal_json_decode(), use \Drupal\Component\Utility\Json::decode().

Issue #1987406 by jenlampton, Petr Illek, forbesgraham, herom, jerdavis, Jon Pugh, sanguis, idflood, ezeedub, shanethehat, joelpittet | Cottser: Node.module - Convert theme_ functions to Twig.