Problem/Motivation
To rename the module to "actions UI" migrations should be moved to system module because entity defined exactly there
Proposed resolution
\Drupal\action\Plugin\migrate\source\Action should be moved to system or migrate_drupal because the action entity defined in system module and module will be renamed to provide UI just to configure actions
Remaining tasks
get agree on move (keep BC)
patch & commit
User interface changes
no
API changes
plugin and some classes will be moved