CS: don't use FQN in docblocks

[jrfnl]

Summary

This PR can be summarized in the following changelog entry:

• Code consistency

Relevant technical choices:

Don't use FQN in docblocks. Use unqualified names instead.

If the file is namespaced and the docblock comment involves a class from another namespace and no use statement is in place yet, add an import use statement.

Note: PHPUnit @covers tags should still be fully qualified (PHPUnit requirement)

Test instructions

This PR can be tested by following these steps:

• N/A