Issue #3336995: Fix .api.php file, descriptions, comments, coding standards

README.txt

list_formatter.api.php

list_formatter.info.yml

list_formatter.module

src/Annotation/ListFormatter.php

src/Plugin/Field/FieldFormatter/ListFormatter.php

src/Plugin/List/DefaultList.php

src/Plugin/List/EntityReferenceList.php

src/Plugin/List/LinkList.php

src/Plugin/List/NumberList.php

src/Plugin/List/OptionsList.php

src/Plugin/List/TaxonomyList.php

src/Plugin/List/TextList.php

src/Plugin/ListFormatterListInterface.php

src/Plugin/ListFormatterPluginManager.php

src/Tests/OutputTest.php

src/Tests/TestBase.php

src/Tests/UITest.php