Issue #3539676: Fix PHPStan issues in HEAD

Closes #3539676

These all look like bugs in PHPStan to me, all these ::id() methods already typehint their return type as : string and they classes are all final.

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Can't reproduce this in the phpstan playground so it might be an issue with phpstan-drupal https://phpstan.org/r/5f28f89c-2c0d-438a-b14a-fd24fd5e74f9