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

Issue #2569083 by dsnopek, tim.plunkett, Wim Leers: Allow passing cacheable metadata to display variants (to enable Panels Everywhere)

Issue #2550941 by dsnopek, tim.plunkett, lslinnet: Allow passing contexts to display variants (to enable Panels Everywhere to use static context and relationships)

Issue #2512062 by dsnopek, tim.plunkett, Wim Leers: VariantInterface extends ConfigurablePluginInterface so PageDisplayVariantSelectionEvent should allow passing configuration to the Variant (to enable Panels Everywhere)