Problem/Motivation
There's a @todo in \Drupal\Core\TypedData\TypedData::__construct() which says that we should use a type hint on DataDefinitionInterface for the $definition argument when #1928868: Typed config incorrectly implements Typed Data interfaces is fixed.
Proposed resolution
Since the referenced issue has been fixed for a while, let's also fix the @todo :)
Remaining tasks
Write a patch.
User interface changes
Nope.
API changes
Nope.
Data model changes
Nope.