Issue #3455354 by pdureau, grimreaper, g4mbini: Add a stories specific discovery

...es/ui_patterns_devel/components/devel/devel.component.yml

...i_patterns_devel/components/devel/devel.default.story.yml

...terns_devel/src/Controller/ComponentValidatorOverview.php

modules/ui_patterns_devel/ui_patterns_devel.info.yml

modules/ui_patterns_legacy/src/ComponentConverter.php

modules/ui_patterns_legacy/src/ComponentWriter.php

...ns_legacy/src/Drush/Commands/UiPatternsLegacyCommands.php

.../ui_patterns_legacy/src/Element/ComponentElementAlter.php

modules/ui_patterns_legacy/src/StoryExtractor.php

modules/ui_patterns_legacy/ui_patterns_legacy.services.yml

modules/ui_patterns_library/docs/plugin_discovery.png

.../ui_patterns_library/src/Controller/LibraryController.php

..._library/src/Discovery/DirectoryWithMetadataDiscovery.php

...ry/src/Discovery/DirectoryWithMetadataPluginDiscovery.php

...ui_patterns_library/src/Element/ComponentElementAlter.php

modules/ui_patterns_library/src/StoryDefault.php

modules/ui_patterns_library/src/StoryInterface.php

modules/ui_patterns_library/src/StoryPluginManager.php

...erns_library/templates/ui-patterns-stories-full.html.twig

modules/ui_patterns_library/ui_patterns_library.services.yml