[TASK] Make base test classes always available

To ease the usage of the core with extensions,
we move the base test classes into a different place
to be able to make them available when typo3/cms is pulled in
as dependency, e.g. for testing extensions or in projects.

This is a non breaking change, as the classes will be available
in any case after that.

By doing so, we can nicely cleanup the .gitattributes file

Resolves: #76425
Releases: master, 7.6
Change-Id: I639f08a4e3e5dd73aa47570d326b72c64452acaf
Reviewed-on: https://review.typo3.org/49159


Reviewed-by: Peter Foerger <pfoerger@mac.com>
Tested-by: Peter Foerger <pfoerger@mac.com>
Reviewed-by: Mathias Brodala <mbrodala@pagemachine.de>
Reviewed-by: Timo Hund <timo.hund@yahoo.com>
Tested-by: Timo Hund <timo.hund@yahoo.com>
Reviewed-by: Helmut Hummel <typo3@helhum.io>
Tested-by: Helmut Hummel <typo3@helhum.io>

.gitattributes

@@ -4,33 +4,4 @@
 /.travis.yml export-ignore
 /Build/ export-ignore
 /dynamicReturnTypeMeta.json export-ignore
-/typo3/sysext/backend/Tests/ export-ignore
-/typo3/sysext/belog/Tests/ export-ignore
-/typo3/sysext/beuser/Tests/ export-ignore
-/typo3/sysext/core/Tests/Acceptance/ export-ignore
-/typo3/sysext/core/Tests/Functional/ export-ignore
-/typo3/sysext/core/Tests/Integrity/ export-ignore
-/typo3/sysext/core/Tests/Legacy/ export-ignore
-/typo3/sysext/core/Tests/Unit/ export-ignore
-/typo3/sysext/dbal/Tests/ export-ignore
-/typo3/sysext/documentation/Tests/ export-ignore
-/typo3/sysext/extbase/Tests/ export-ignore
-/typo3/sysext/extensionmanager/Tests/ export-ignore
-/typo3/sysext/felogin/Tests/ export-ignore
-/typo3/sysext/fluid/Tests/ export-ignore
-/typo3/sysext/form/Tests/ export-ignore
-/typo3/sysext/frontend/Tests/ export-ignore
-/typo3/sysext/impexp/Tests/ export-ignore
-/typo3/sysext/indexed_search/Tests/ export-ignore
-/typo3/sysext/install/Tests/ export-ignore
-/typo3/sysext/lang/Tests/ export-ignore
-/typo3/sysext/lowlevel/Tests/ export-ignore
-/typo3/sysext/recordlist/Tests/ export-ignore
-/typo3/sysext/recycler/Tests/ export-ignore
-/typo3/sysext/reports/Tests/ export-ignore
-/typo3/sysext/rsaauth/Tests/ export-ignore
-/typo3/sysext/saltedpasswords/Tests/ export-ignore
-/typo3/sysext/scheduler/Tests/ export-ignore
-/typo3/sysext/setup/Tests/ export-ignore
-/typo3/sysext/sv/Tests/ export-ignore
-/typo3/sysext/workspaces/Tests/ export-ignore
+/typo3/sysext/*/Tests/ export-ignore