Issue #2377115 by mglaman: Replace all instances of entity_load('field_config') and entity_load_multiple('field_config') with static method calls

Issue #2340667 by YesCT, Pedro Lozano, alexpott, martin107: Protect Drupal\Core\Language\Language::id, and use getId().

Issue #2312093 by alexpott, yched, andypost, swentel | xjm: Rename FieldInstanceConfig to FieldConfig.

Issue #2336177 by alexpott, YesCT: Fixed ConfigurableLanguage cannot be created/removed directly, integrate language_save() and language_delete().

Issue #2287727 by yched, swentel, alexpott: Rename Field[instance]Config classes and entity types (again).

Issue #2143291 by plach, alexpott, xjm, effulgentsia, pwolanin, swentel | yched: Clarify handling of field translatability.

Issue #2183231 by tstoeckler, plach, jessebeach, fago, Berdir, xjm, mauzeh: Make ContentEntityDatabaseStorage generate static database schemas for content entities.

Issue #2095303 by swentel, plopesc, Berdir, claudiu.cristea, yched: Rename 'field_entity' to 'field_config' and 'field_instance' to 'field_instance_config'.

Issue #2167109 by Berdir, sun, alexpott, ACF, acrollet, adamdicarlo, Albert Volkman, andreiashu, andyceo, andypost, anenkov, aspilicious, barbun, beejeebus, boombatower, cam8001, chriscalip, chx, cosmicdreams, dagmar, damiankloip, dawehner, deviance, disasm, dixon_, dstol, ebrowet, Gábor Hojtsy, heyrocker, Hydra, ianthomas_uk, japicoder, jcisio, jibran, julien, justafish, jvns, KarenS, kbasarab, kim.pepper, larowlan, Lars Toomre, leschekfm, Letharion, LinL, lirantal, Lukas von Blarer, marcingy, Mike Wacker, mrf, mtift, mtunay, n3or, nadavoid, nick_schuch, Niklas Fiekas, ParisLiakos, pcambra, penyaskito, pfrenssen, plopesc, Pol, Rok Žlender, rvilar, swentel, tim.plunkett, tobiasb, tsvenson, typhonius, vasi1186, vijaycs85, wamilton, webchick, webflo, wizonesolutions, xjm, yched, YesCT, znerol: Remove Variable subsystem.

Issue #1862202 by plach, Berdir, katbailey, ParisLiakos, alexpott, chx, sun, larowlan, Gábor Hojtsy, cosmicdreams, vijaycs85, YesCT, penyaskito, andypost, Albert Volkman, joelpitett: Objectify the language system.

Issue #2018319 by yched, swentel, pcambra: Remove field_read_field(s)() and field_read_instance(s) in favor of entity_load() and entity_load_multiple_by_properties().

Issue #2076445 by plach, andypost, yched, Gábor Hojtsy: Make sure language codes for original field values always match entity language regardless of field translatability.