Issue #3389510 by catch, tedbow, dww, Gábor Hojtsy: Split up update semver tests

.../tests/src/Functional/UpdateSemverContribBaselineTest.php

...unctional/UpdateSemverContribSecurityAvailabilityTest.php

...date/tests/src/Functional/UpdateSemverContribTestBase.php

...ate/tests/src/Functional/UpdateSemverCoreBaselineTest.php

...c/Functional/UpdateSemverCoreSecurityAvailabilityTest.php

...s/src/Functional/UpdateSemverCoreSecurityCoverageTest.php

...ules/update/tests/src/Functional/UpdateSemverCoreTest.php

.../update/tests/src/Functional/UpdateSemverCoreTestBase.php

...ules/update/tests/src/Functional/UpdateSemverTestBase.php

...te/tests/src/Functional/UpdateSemverTestBaselineTrait.php

.../Functional/UpdateSemverTestSecurityAvailabilityTrait.php