Issue #3565094 by dydave: Added 'declare(strict_types=1)' to all PHP files.

David Suissarequested to merge
issue/admin_toolbar-3565094:3565094-add-declarestricttypes into 3.x

https://www.drupal.org/project/admin_toolbar/issues/3565094

Added declare(strict_types=1) to all PHP files.

Merge request reports