Issue #2949177 by tim.plunkett, samuel.mortenson, mark_fullmer, tedbow, EclipseGc, andypost: Introduce a service that returns filtered plugin definitions

Issue #2660124 by tim.plunkett, samuel.mortenson, phenaproxima, tstoeckler, yoroy, dead_arm, xjm, Manuel Garcia, EclipseGc, larowlan, DyanneNova, tedbow: Dynamically build layout icons based on well formed config

Issue #2902723 by mfernea, ccjjmartin: Fix 'Drupal.Commenting.FunctionComment.ReturnCommentIndentation' coding standard

Issue #2834025 by tim.plunkett, Manuel Garcia, swentel, japerry: Mark Layout Discovery as a stable module

Issue #2851648 by tim.plunkett, jibran: Layout regions should be in the order defined by the definition

Issue #2851574 by tim.plunkett, mpdonadio: DependentPluginDefinitionInterface and DependentPluginDefinitionTrait should be in Drupal\Core not Drupal\Component

Issue #2821189 by tim.plunkett, tstoeckler: Allow object-based plugin definitions to be processed in DerivativeDiscoveryDecorator

Issue #2822752 by tim.plunkett, jibran: Allow object-based plugin definitions to be created by non-annotated discovery

Issue #2821191 by tim.plunkett, tstoeckler, jibran: Allow object-based plugin definitions to be processed in PluginDependencyTrait

Issue #2824655 by tim.plunkett: Plugin definitions should store their class in a consistent manner (without leading slashes)

Issue #2559825 by tim.plunkett, Antti J. Salminen, lauriii, aspilicious, alexpott: Preprocess functions from base hooks not triggered for theme hooks not using the __  pattern

Issue #2818653 by tim.plunkett, tstoeckler, jibran: Allow object-based plugin definitions to be processed in DefaultPluginManager::findDefinitions()

Issue #2296423 by tim.plunkett, dsnopek, swentel, Manuel Garcia, tedbow, alexpott, xjm, andypost, dawehner, effulgentsia, Berdir, jhedstrom, catch, benjy, jibran, Wim Leers, tstoeckler, larowlan, webchick: Implement layout plugin type in core