Issue #1512424 by Xano, YesCT, RobLoach: Add a LanguageInterface, and property setters/getters to Language class.

Issue #2217783 by mondrake: Remove $extension and $mimeType from Image, use image_type_to_xxx function in the getters instead.

Issue #2154711 followup by by jlbellido: Move entity_get_(form/view)_mode_options() functions to EntityManager and add get(Form/View)ModeOptions() methods.

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

Issue #70719 by neclimdul, superspring, longwave, kscheirer, InternetDevels: Add Unicode::ucwords() and Unicode::lcfirst() implementation and make use of them in core.

Issue #1662954 by balis_m, mjonesdinero, kalpaitch, IshaDakota, kerasai, ckrina, BarisW | ZenDoodles: Use less-specific tabledrag selectors.

Issue #1808248 by alexpott, beejeebus, tayzlor, Nitesh Sethia: Add a separate module install/uninstall step to the config import process.

Issue #2224861 by Wim Leers, dawehner, pwolanin: Cache SystemMenuBlock and BookNavigationBlock per active trail (currently cached per URL, this breaks on very long URLs).

Issue #2219689 followup by damiankloip: Separate out logic for getPluginTypes/viewsHandlerTypes from ViewExecutable.

Issue #2209145 by slashrsm, fgm, chx: Move all path alias SQL queries to a single storage controller.

Issue #2219689 by damiankloip: Separate out logic for getPluginTypes/viewsHandlerTypes from ViewExecutable.

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

Broke update.php.

This reverts commit 10b03890.

Issue #1709960 by Berdir, zserno, jessebeach | joachim: Declare a maximum length for entity and bundle machine names.

Issue #2231945 by visabhishek, cs_shadow, fran seva | tstoeckler: FieldableDatabaseEntityStorageTest.php is misnamed.

Issue #2002246 by tompagabor, floretan, lauriii, pakmanlh, rbomhof | pixelite: Capitalize operations links in the comment and taxonomy term admin UI.

Issue #2227687 by cs_shadow, Cottser: Slightly ugly error message if a module is incompatible with the version of core and the PHP version.

Issue #1081192 by wojtha, klausi, larowlan, nedjo, Heine: Verify peer on HTTPS if cURL available (but be careful of built-in cert bundles in the codebase).

Issue #2229931 by xjm, Berdir: Improve documentation related to config object filename component limits

Issue #2228921 by sun: Consolidate system.module + system.theme + system.theme.disabled into core.extension config.

Issue #2200333 by Xano: Content_translation_view_access() is invoked as a hook_ENTITY_TYPE_access() hook implementation.