[TASK] Make a resource storage driver accessible

The method "getDriver" of a resource storage is not public. This
inhibits any extension (even core extensions like import/export) to
perform actions which are custom for a special type of driver. Of
course it makes sense to obfuscate the driver layer to most
applications and extensions, but in some cases it is handy
to directly talk to a driver.

Releases: master
Resolves: #72728
Change-Id: If01f3ca6208846b9520e2ef4af2a9483e11f6d88
Reviewed-on: https://review.typo3.org/45933


Reviewed-by: Markus Klein <markus.klein@typo3.org>
Tested-by: Markus Klein <markus.klein@typo3.org>
Reviewed-by: Anja Leichsenring <aleichsenring@ab-softlab.de>
Tested-by: Anja Leichsenring <aleichsenring@ab-softlab.de>