(cherry picked from commit 2b5bca51)

Issue #2867960 by Eric_A, Mile23, Jo Fitzgerald, mpdonadio: Merge Component composer.json files to account for them during build

Issue #2935137 by el7cosmos, Mixologic: License "GPL-2.0+" is a deprecated SPDX license identifier, use "GPL-2.0+-only" or "GPL-2.0+-or-later" instead

Issue #2927806 by alexpott, mondrake, jibran, Mile23: Use PHPUnit 6 for testing when PHP version >= 7.2

Issue #2886279 by dawehner, alexpott, drpal, zaporylie, Wim Leers, neclimdul, Mile23, Chi: Add PHPCS and PHPCBF as Composer scripts

This reverts commit 7c486399.

Issue #2851661 by alexpott, dawehner, xjm: Ensure that we're using the right ruleset for coding standards checking

Issue #2866109 by Eric_A: Add composer installer-paths for drupal-custom-modules/themes before 8.3.0

Issue #2758737 by Mixologic, amateescu, ndf, webflo, Mile23, bojanz: Add a packages.drupal.org to root composer.json

Issue #2744463 by Mile23, dawehner, pfrenssen, joelpittet, tstoeckler, alexpott, klausi: Add phpcs, coder 8.2.8 as --dev requirements for drupal/core

Issue #2585165 by pwolanin, alexpott, tarekdj, geertvd, dawehner, greggles: Don't include vendor test code (especially mink) in the Drupal webroot

Issue #2380389 by webflo, Mile23, davidwbarratt, timmillwood, hussainweb, tstoeckler, bojanz, yched, MKorostoff, alexpott, webchick: Use a single vendor directory in the root

Issue #2400407 by DuaelFr, webchick, hussainweb, klausi, dawehner, cilefen, catch, kim.pepper, iMiksu, MustangGB: [meta] Ensure vendor (PHP) libraries are on latest stable release

Issue #2406681 by tstoeckler, hussainweb, alexpott, ParisLiakos, almaudoh, tadityar: Add an autoload.php in the repo root to control the autoloader of front controllers

Issue #1975220 by davidwbarratt, tstoeckler, mradcliffe, RobLoach, Mile23, hussainweb: Allow a Composer user to manage Drupal, modules, and PHP dependencies with a custom root composer.json

Issue #2234277 by cilefen, hussainweb, Xano, netlooker, martin107: Composer update (includes security fixes).