Issue #3321282 by omkar.podey, Wim Leers, tedbow: Add 'declare(strict_types = 1)' where needed

package_manager/src/Validator/LockFileValidator.php

package_manager/src/Validator/MultisiteValidator.php

...ager/src/Validator/OverwriteExistingPackagesValidator.php

package_manager/src/Validator/PendingUpdatesValidator.php

...ger/src/Validator/PreOperationStageValidatorInterface.php

package_manager/src/Validator/SettingsValidator.php

package_manager/src/Validator/StagedDBUpdateValidator.php

package_manager/src/Validator/SupportedReleaseValidator.php

package_manager/src/Validator/SymlinkValidator.php

...age_manager/src/Validator/WritableFileSystemValidator.php

package_manager/src/Validator/XdebugValidator.php

...ger/tests/modules/package_manager_bypass/src/Beginner.php

.../package_manager_bypass/src/BypassedStagerServiceBase.php

...er/tests/modules/package_manager_bypass/src/Committer.php

...anager_bypass/src/PackageManagerBypassServiceProvider.php

.../tests/modules/package_manager_bypass/src/PathLocator.php

...nager/tests/modules/package_manager_bypass/src/Stager.php

...ts/modules/package_manager_test_api/src/ApiController.php

...ckage_manager_test_release_history/src/TestController.php

...er_test_validation/src/EventSubscriber/TestSubscriber.php