Move tests to PSR-4

apps/files_sharing/tests/API/Share20OCSTest.php

apps/files_sharing/tests/API/ShareesTest.php

apps/files_sharing/tests/ActivityTest.php

apps/files_sharing/tests/ApiTest.php

apps/files_sharing/tests/BackendTest.php

apps/files_sharing/tests/CacheTest.php

apps/files_sharing/tests/CapabilitiesTest.php

...sharing/tests/Controllers/ExternalShareControllerTest.php

apps/files_sharing/tests/Controllers/ShareControllerTest.php

apps/files_sharing/tests/DeleteOrphanedSharesJobTest.php

apps/files_sharing/tests/EncryptedSizePropagationTest.php

apps/files_sharing/tests/EtagPropagationTest.php

apps/files_sharing/tests/ExpireSharesJobTest.php

apps/files_sharing/tests/External/CacheTest.php

apps/files_sharing/tests/External/ManagerTest.php

apps/files_sharing/tests/External/ScannerTest.php

apps/files_sharing/tests/ExternalStorageTest.php

apps/files_sharing/tests/GroupEtagPropagationTest.php

apps/files_sharing/tests/HelperTest.php

apps/files_sharing/tests/LockingTest.php