The base implementation says it can accept an array with a single
element, but the subclasses only had `string` in the docblock (although
they could handle the array case). Hence, replace docblocks in
subclasses with @inheritDoc to copy the parent description and avoid
such discrepancies in the future.
Plus, change `array` to `string[]` for better type inference.
Change-Id: Ica9929fd50f31d8d5f0e29f7c60364086ea39ae5
Moved classes in Export.php to seperate files in the new directory
includes/export/ and updated autoload.php to these new locations.
Bug: T122531
Change-Id: Idd3bba5a85d65c952f2ff503bea2ca76624c9b7f
