Properties with unknown classes as its type

Problem/Motivation

After install and run phpstand-drupal I got a report with many problems related to "Properties with unknown classes as its type".

See Writing better Drupal code with static analysis using PHPStan for more information about the tool.

Proposed resolution

Fix the problems related to properties with unknown classes as its type and create a patch.

Remaining tasks

None.

User interface changes

None.

API changes

None.

Data model changes

None.

Release notes snippet

None.