Issue #3134648 by alexpott, dww, greg.1.anderson, hussainweb, catch, xjm: Don't pin the composer/installers version in drupal/core-recommended

Issue #3043471 by longwave, catch, Wim Leers, xjm: Replace the DiactorosFactory message factory in symfony/psr-http-message-bridge with a PSR-17 compliant message factory

Issue #3020296 by alexpott, longwave, bradjones1, catch, Berdir, gapple: Remove Symfony's classloader as it does not exist in Symfony 4

Issue #3109261 by longwave, Gábor Hojtsy: Update composer dependencies on 9.0.x following PHP 7.3 requirement

Issue #3104354 by longwave, TravisCarden, xjm, catch, alexpott, Wim Leers: Update Laminas components including Diactoros

Issue #3104015 by TravisCarden, alexpott, longwave, Spokje, fgm, catch, xjm, Berdir, Bruno Vincent: Replace ZendFramework/* dependencies with their Laminas equivalents

Issue #3104265 by longwave, catch, xjm, TravisCarden: Update Composer dependencies on Doctrine components in 9.0.x

Issue #3091418 by Manuel Garcia, jibran, tedbow, TravisCarden, xjm, greg.1.anderson, Gábor Hojtsy, catch, Mile23, Berdir, hussainweb: Update composer dependencies on 9.0.x

SA-CORE-2019-012 by samuel.mortenson, larowlan, pwolanin, Sam152, Jasu_M, David_Rothstein, michieltcs, Ayesh, alexpott, xjm, vijaycs85, mcdruid

Issue #2901363 by alexpott, Mile23, shubham.prakash, prithvi1972, Jaesin, cilefen, borisson_, runeasgar: Move easyrdf/easyrdf to require-dev

Issue #3088754 by mikelutz, alexpott, Eric_A, catch, Krzysztof Domański: Update to Drupal 9 to Symfony 4.4.0

Issue #3090906 by alexpott, greg.1.anderson, ravi.shankar, xjm, Mixologic, Mile23: self.version in metapackages considered harmful

Issue #3041076 by alexpott, shaal, Gábor Hojtsy, lauriii, Wim Leers, catch, Cottser, jibran, andypost, znerol, xim, joelpittet, effulgentsia: Update Drupal 9 to Twig 2

Issue #3087626 by greg.1.anderson, Mixologic, jibran, Mile23, alexpott, xjm: Convert drupal/core-recommended & c. into a subtree split