This reverts commit a879c616.

Issue #3423920 by DanielVeza, smustgrave, acbramley, bradallenfisher, larowlan, alexpott: Custom Blocks with Layout Builder Enabled No Longer Use Front End Theme

Issue #3442864 by dww, catch: [regression] 404 for misc/throbber-active.gif / misc/loading-small.giff

Issue #3439981 by fago, ericgsmith, petar_basic, acbramley: Uploading a file to media library flushes theme registry

Issue #3414398 by catch, Berdir: AssetResolver::getJsAssets() and AssetResolver::getCssAssets()  can repeatedly try to calculate the same set of assets

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

Issue #3442532 by smustgrave, andypost, pradhumanjain2311, quietone: Removed deprecated code in views module

Issue #3432882 by kim.pepper, Satane, andypost, alexpott, longwave: Remove deprecated code in File module

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

Issue #3439369 by fromme, quietone, pradhumanjain2311, smustgrave, alexpott: Remove deprecated code in migration system

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 #3437839 by catch, Luke.Leber, thejimbirch: Only send libraries with aggregate URLs that have the aggregate type included

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

Issue #3439831 by thebumik, pradhumanjain2311, vensires: Fix Config tests that rely on UID1's super user behavior

Issue #3238868 by ahsannazir, smustgrave: Refactor some uses of the jQuery parents function to use vanillaJS

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 #3438771 by amateescu, Michelle, smustgrave: Newly added menu links are invisible until published

Issue #3307519 by amateescu, Darren Oh, s_leu, catch: The toolbar workspace switcher is not redirecting to the current page

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

Issue #3441660 by longwave: [PHPUnit 10] Provide a static alternative to @dataproviders using PHPUnit mocks in MailHandlerTest

Issue #3261653 by Spokje, catch, larowlan, quietone, kim.pepper, smustgrave, andypost, lauriii: Remove Forum module