Tx_Extbase_Persistence_Storage_Typo3DbBackend::parseQuery expects a
Tx_Extbase_Persistence_QueryInterface and then calls getSource on it.
One way to make this clean is to change
Tx_Extbase_Persistence_QueryInterface to provide the getSource method.

Releases: 4.7, 4.8
Fixes: #34916

Change-Id: Ic84a6897c7f46048e4967669712d7afcbc4df069