[TASK] Doctrine: migrate ext:backend/Clipboard/Clipboard

Resolves: #75770
Releases: master
Change-Id: I8b4eb42763ca30b2c099371b7a8206d8098c2f79
Reviewed-on: https://review.typo3.org/47774


Reviewed-by: Wouter Wolters <typo3@wouterwolters.nl>
Reviewed-by: Michiel Roos <michiel@maxserv.com>
Tested-by: Michiel Roos <michiel@maxserv.com>
Reviewed-by: Morton Jonuschat <m.jonuschat@mojocode.de>
Tested-by: Morton Jonuschat <m.jonuschat@mojocode.de>