Issue #2889600 by droplet, drpal, Gábor Hojtsy, effulgentsia, Wim Leers: [regression] Restore \LocaleJavascriptTranslationTest test coverage and keep testing processed JS file

Issue #2815077 by drpal, mradcliffe, effulgentsia, mpdonadio, nod_, droplet, alexpott, nedjo, tizzo, David_Rothstein, pfrenssen: Adopt airbnb javascript style guide v13 as new baseline javascript coding standards for Drupal 8 core and contrib