Issue #3395954 by pdureau: Improve legacy module coverage

modules/ui_patterns_legacy/src/ComponentConverter.php

modules/ui_patterns_legacy/src/ComponentDiscovery.php

modules/ui_patterns_legacy/src/ComponentWriter.php

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

modules/ui_patterns_legacy/src/Element/Pattern.php

modules/ui_patterns_legacy/src/Element/PatternPreview.php

modules/ui_patterns_legacy/src/PropConverter.php

modules/ui_patterns_legacy/src/RenderableConverter.php

modules/ui_patterns_library/src/Element/ComponentStory.php

src/Element/ComponentElement.php

src/Plugin/UiPatterns/PropType/LinksPropType.php

src/Sdc/UiPatternsSdcPluginManager.php