Issue #2270815 by vijaycs85, Gábor Hojtsy, nvinayvinay: Make schema testing code available as generic API.
Issue #2216557 by jhodgdon, mongolito404, Berdir: Fill in @defgroup/topic docs for Testing overview.
Issue #2216533 by jhodgdon: Fill in topic/@defgroup docs for Entity API overview.
Issue #2216553 by jhodgdon, fago: Fill in @defgroup/topic docs for Typed Data.
Issue #2287193 by alexpott: Fixed checkConfigSchema() can fail to report errors.
Issue #2285795 by Gábor Hojtsy: Fixed Drupal 8 loads alpha2 translations instead of alpha12.
Merge remote-tracking branch 'origin/8.x' into mink-testing-2232861-larowlan
Tagged hack with @todo