[!!!][TASK] Doctrine: migrate ext:backend/Tree

Releases: master
Resolves: #75645
Change-Id: I4ee542e4c939388cfccdb896ff1e38e849965849
Reviewed-on: https://review.typo3.org/47693


Reviewed-by: Morton Jonuschat <m.jonuschat@mojocode.de>
Tested-by: Morton Jonuschat <m.jonuschat@mojocode.de>
Reviewed-by: Wouter Wolters <typo3@wouterwolters.nl>
Reviewed-by: Daniel Goerz <ervaude@gmail.com>
Reviewed-by: Frank Naegler <frank.naegler@typo3.org>
Tested-by: Frank Naegler <frank.naegler@typo3.org>