Issue #3336255 by tedbow, Wim Leers: Explore simplifying our fixture manipulation classes

...es_extensions/tests/src/Functional/DisplayUpdatesTest.php

...ules/fixture_manipulator/fixture_manipulator.services.yml

...ts/modules/fixture_manipulator/src/FixtureManipulator.php

...dules/fixture_manipulator/src/StageFixtureManipulator.php

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

package_manager/tests/src/Kernel/FixtureManipulatorTest.php

...sts/src/Kernel/OverwriteExistingPackagesValidatorTest.php

...manager/tests/src/Kernel/PackageManagerKernelTestBase.php

...anager/tests/src/Kernel/SupportedReleaseValidatorTest.php

package_manager/tests/src/Traits/FixtureManipulatorTrait.php

tests/src/Functional/AutomaticUpdatesFunctionalTestBase.php

tests/src/Functional/DeleteExistingUpdateTest.php

tests/src/Functional/StagedDatabaseUpdateTest.php

tests/src/Functional/StatusCheckTest.php

tests/src/Functional/StatusCheckerRunAfterUpdateTest.php

tests/src/Functional/SuccessfulUpdateTest.php

tests/src/Functional/UpdateCompleteMessageTest.php

tests/src/Functional/UpdateFailedTest.php

tests/src/Functional/UpdateLockTest.php

tests/src/Kernel/CronUpdaterTest.php