Revert "Issue #2388749 by alexpott, adci_contributor, ParisLiakos: Register symfony's mime guessers if they are supported"

This reverts commit 4dae1d99.

Issue #2388749 by alexpott, adci_contributor, ParisLiakos: Register symfony's mime guessers if they are supported

Issue #2142653 by corbacho, sqndr, LewisNyman, floretan, BarisW, G-raph, JamesLefrère, lokapujya, LoMo, Outi: Change default logo filetype to .svg and add an SVG version of Druplicon

Issue #2392319 by alexpott, effulgentsia: Config objects (but not config entities) should by default be immutable

Issue #2040135 by Wim Leers, Berdir: Caches dependent on simple config are only invalidated on form submissions

Issue #2151469 by rpayanm, lokapujya, JeroenT, alansaviolobo, Richard Damon, pflame, ianthomas_uk: Clean-up usage of deprecated list_themes() and _system_rebuild_theme_data() in favor of theme_handler service.

Issue #1759090 by andrewmacpherson, InternetDevels, jjcarrion: Remove redundant CSS from theme settings form

Issue #1869476 by rteijeiro, LewisNyman, lauriii, Wim Leers, mdrummond, swentel, hosef, cbiggins, larowlan, sun, EclipseGc, Gábor Hojtsy: Convert global menus (primary links, secondary links) into blocks.

Issue #2340123 by Wim Leers: Setting cache tags can be tricky: use strings instead of nested arrays to improve DX.

Issue #2337709 by tim.plunkett: Convert form_state_values_clean() to FormStateInterface::cleanValues().

Issue #2308821 by tim.plunkett: Replace FormErrorInterface with $form_state->setErrorByName() and $form_state->setError().

Issue #2124957 by Wim Leers, catch: Replace 'content' cache tag with 'rendered' and use it sparingly.

Issue #2239065 by tim.plunkett | webchick: Overridden config bleeding through to configuration forms.

Issue #2185617 by Wim Leers, voidberg, drifter: Each page cache entry should have a theme cache tag.

Issue #2210197 by sun, longwave, Sutharsan: Remove public access to Extension::$type, ::$name, ::$filename.

Revert "Issue #2210197 by sun, longwave: Remove public access to Extension::$type, ::$name, ::$filename." Broke 'drush en simpletest' on testbots

This reverts commit 2c51074d.

Issue #2098119 by beejeebus, alexpott, chx: Replace config context system with baked-in locale support and single-event based overrides.

Issue #2145007 by tim.plunkett, h3rj4n: Convert form_set_error() in FormBase classes to use FormErrorInterface.

Issue #2102125 by dawehner, tim.plunkett, neclimdul, pwolanin, YesCT, damiankloip, Tim Bozeman: Big Local Task Conversion.

Issue #2089627 by tim.plunkett: Move \Drupal\system\SystemConfigFormBase to \Drupal\Core\Form\ConfigFormBase.

Issue #1856766 by chx, Berdir, heyrocker, kim.pepper: Convert file_public_path() to the new settings system (make it not configurable via UI or YAML).