Issue #1472946 by gnuget, andypost, mmrares, sidharthap, kiamlaluno, Himanshu5050, dineshkumares, amit.drupal: Remove usages of deprecated function drupal_realpath() throughout core functions

Issue #2873696 by nvexler, wengerk, gido, Jo Fitzgerald, xjm: Add @internal to core classes, methods, properties to Form Classes

Issue #2482783 by dmsmidt, alexpott, mgifford, 20th, Sutharsan, Jo Fitzgerald, tim.plunkett, dandaman, xjm: File upload errors not set or shown correctly

Issue #1862892 by oriol_e9g, joseph.olstad, vaplas, G.I.Joe, leopathu, peterpoe, cilefen, xjm, larowlan: When a theme has a managed_file field and a submit callback, call to undefined function error is thrown

Issue #2776975 by joelpittet, dawehner, tim.plunkett, xjm, pfrenssen: March 3, 2017: Convert core to array syntax coding standards for Drupal 8.3.x RC phase

Issue #2048887 by pguillard, yoroy, Anul, rpayanm, meeli, ifrik, Bojhan, xjm: Cleanup user interface text on appearance/settings

Issue #2285311 by joelpittet, tomatkins, susannecoates: Theme's "Path to custom logo" always validated even if "Use the default logo" is set

Issue #2665992 by alexpott, klausi, heykarthikwithu, xjm, tstoeckler: @file is not required for classes, interfaces and traits

Issue #2620442 by Lendude: Theme logo upload settings are shown even if the file module is not installed

Issue #2620176 by joelpittet, markcarver, hatuhay: Logo image settings form is broken, breaks per-theme overrides and can result in data loss

Issue #2574975 by alexpott, Cottser, izus: Allow (base-)themes to be excluded from the UI (e.g. blocks, Appearance)

Issue #1006266 by alexpott, ryanissamson, Tor Arne Thune, CrookedNumber: Saving theme-specific theme settings with no logo creates Undefined index error when file module enabled

Issue #2005546 by mdrummond, joelpittet, Manuel Garcia, lauriii, lokapujya, epari.siva, hosef, rpayanm, emma.maria, HOG, zetagraph, wmortada, rteijeiro, Cottser, hussainweb, madhavvyas: Use branding block in place of page template branding variables (site name, slogan, site logo)

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.