Issue #2308967 by martin107: Fix spelling errors
Issue #2308707 by eojthebrave: Fix annotation class reference in field.api.php
Issue #2308699 by eojthebrave: Fix documentation of WidgetBaseInterface::formElement method
Issue #2308695 by eojthebrave: Fix typo
Issue #2290275 by chx: Add information to migrate plugin classes and interfaces for developers