Revert "Issue #3443493 by smustgrave, Gábor Hojtsy, mikelutz: Remove deprecated code from lib/State and lib/Session"

This reverts commit d494e667.

Issue #3443493 by smustgrave, Gábor Hojtsy, mikelutz: Remove deprecated code from lib/State and lib/Session

Issue #3440043 by mondrake, longwave, larowlan, alexpott: Stop triggering a warning in MySQL's TransactionManager rollback

Issue #3441394 by quietone, smustgrave, pradhumanjain2311, catch: Remove deprecated code in utilities

Issue #3442713 by smustgrave, catch, Binoli Lalani, longwave: Remove deprecated code from the entity system

Issue #3443037 by alexpott, catch, kristiaanvandeneynde, Taran2L, longwave: Super user access policy and the installer

Issue #3443300 by mondrake: Fix remaining return*() methods of class PHPUnit\Framework\TestCase deprecated in PHPUnit 10

Issue #3443248 by alexpott: Can't log out on translated site in tests - causes issues for 10.3 umami test

Issue #3416700 by catch, penyaskito, lamp5: Handle invalid compressed ajax_page_state more gracefully

Issue #3432868 by smustgrave, obsidian_, longwave, quietone, mstrelan, catch: Remove deprecated code from user module

Issue #144538 by acbramley, tuutti, Damien Tournoud, alexpott, solideogloria, Xano, TwoD, damiankloip, smustgrave, pameeela, deviantintegral, L_VanDamme, daften, karishmaamin, g.oechsler, larowlan, klausi, sun, Fabianx, andypost, dawehner, kwinters, greggles, Wim Leers, grendzy, pwolanin, alexanderpas, drumm, Chi: User logout is vulnerable to CSRF

Issue #1561214 by mfb, sun, fietserwin, drzraf, sdrycroft, nicxvan: Bootstrap sets C locale, but does not set UTF-8 character encoding

Issue #3343153 by samit.310@gmail.com, andypost, smustgrave, alexpott: Remove deprecated code from \Drupal\Core\Url

Issue #3425294 by thhomas, longwave, saurabh rawat, quietone, mstrelan: Remove deprecations for UrlGenerator methods

Issue #3440424 by alexpott: Inconsistent behaviour with drupalGet() when site is installed in a subdirectory

Issue #3439925 by simonbaese, smustgrave, vensires: Fix Core tests that rely on UID1's super user behavior

Issue #3441718 by mondrake: Fix string array keys in data sets returned by data provider methods that do not match the parameter names in Unit tests

Issue #3414563 by quietone, catch, smustgrave, andypost, Spokje: Add new 10.3.x database dump fixtures, without modules deprecated for removal in 11.x

Issue #3437325 by narendraR, phenaproxima, alexpott, Wim Leers: Add validation constraints to system.date

Issue #3440170 by mxr576, quietone, smustgrave, longwave, larowlan: Forked DocParser incorrectly parses ::class notations

Issue #3439824 by quietone: Remove deprecated code from assertion, eventdispatcher and plugin components