Issue #2575615 by alexpott, pwolanin, stefan.r, catch, dawehner, effulgentsia, xjm, David_Rothstein, iMiksu, lauriii, joelpittet: Introduce HtmlEscapedText and remove SafeMarkup::setMultiple() and SafeMarkup::getAll() and remove the static safeStrings list

Issue #2426969 by David_Rothstein, joelpittet, dawehner: Dynamic redirects are no longer possible in the batch API (breaks updating existing modules or themes with the Update Manager)

Issue #2351015 by plach, effulgentsia, Wim Leers, dawehner, martin107, damiankloip, cilefen, Fabianx, catch, pwolanin, Damien Tournoud, znerol, YesCT, larowlan: URL generation does not bubble cache contexts

Issue #2407195 by Wim Leers, Fabianx, joelpittet, lauriii, Crell: Move attachment processing to services and per-type response subclasses

Revert "Issue #1986330 by subhojit777, marcelodornelas, wheatpenny, kasperg, timaholt, stefank, AkshayKalose, develCuy, valthebald, moymilo, YesCT, dawehner, tstoeckler: When Batch ID doesn't exist, Drupal should emit a 404"

Somehow broke testbot/HEAD. Reverting for now.

This reverts commit 30432a03.

Issue #1986330 by subhojit777, marcelodornelas, wheatpenny, kasperg, timaholt, stefank, AkshayKalose, develCuy, valthebald, moymilo, YesCT, dawehner, tstoeckler: When Batch ID doesn't exist, Drupal should emit a 404

Issue #2364157 by mpdonadio, dawehner, martin107, Berdir, pcambra, naveenvalecha, tim.plunkett: Replace most existing _url calls with Url objects

Issue #2367743 by rpayanm, Miroling, YesCT, ianthomas_uk, shadik, gaurav.pahuja: Remove usages of drupal_form_submit() and update documentation

Issue #2378095 by Wim Leers, Devin Carlson: Convert all remaining attached individual CSS/JS assets to attached asset libraries

Issue #2362227 by dawehner, mpdonadio, znerol, tim.plunkett, skipyT: Replace all instances of current_path()

Issue #2328111 by dawehner, martin107, neclimdul: Replace most instances of the DRUPAL_ROOT constant with the app.root container parameter.

Issue #2350877 by dawehner, Wim Leers, hussainweb: Deprecate/rename drupal_add_feed(), drupal_add_html_head(), drupal_add_html_head_link(), drupal_add_http_header(), and allow to be set declaratively in #attached.

Issue #2343661 by larowlan, tim.plunkett | xjm: Rename l() to _l() and url() to _url(), and document replacements.

Issue #2343759 by pwolanin, larowlan, dawehner, tim.plunkett, effulgentsia, xjm, Wim Leers: Provide an API function to replace url()/l() for external urls.

Issue #2340251 by iMiksu, alexpott, tim.plunkett, dawehner, Wim Leers: Remove most remaining url() calls.

Issue #2335659 by tim.plunkett, dawehner, effulgentsia, sun: Remove FormState ArrayAccess usage from core.

Issue #2318099 by tim.plunkett: Replace $form_state['complete_form'] with $form_state->getCompleteForm().

Issue #2149197 by penyaskito, mikey_p, vijaycs85, herom: Replace format_interval with \Drupal::service('date')->formatInterval().

Issue #1825952 by Fabianx, joelpittet, bdragon, heddn, chx, xjm, pwolanin, mikey_p, ti2m, bfr, dags, cilefen, scor, mgifford: Turn on twig autoescape by default

Issue #2299421 by amitgoyal, joshi.rohit100: Remove all usage of drupal_build_form() as deprecated and replaced by FormBuilderInterface::buildForm().

Revert "Issue #2218039 by sun, dawehner: Render the maintenance/install page like any other HTML page."

Broke update.php.

This reverts commit 10b03890.

Issue #2203407 by nod_, sun: Replace #attached library array values with provider-namespaced strings.

Issue #2192649 by sun, chakrapani, sidharthap: Remove drupal_set_title() from installation and update process.

Issue #1996238 by sun, nod_, damiankloip, Wim Leers, longwave, alexpott, Xano, mdrummond, Mark Carver, Jeff Burnz, highrockmedia, joelpittet, et al: Replace hook_library_info() by *.libraries.yml file.