[TASK] Doctrine: Migrate TableFlexFormToTtContentFieldsUpdate

Change-Id: I876f68da7ca9799a03ca14b5df9032eb8bf6e430
Resolves: #77504
Releases: master
Reviewed-on: https://review.typo3.org/49486


Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Bamboo TYPO3com <info@typo3.com>
Reviewed-by: Tobias Adolph <mail@tobiasadolph.de>
Tested-by: Tobias Adolph <mail@tobiasadolph.de>
Reviewed-by: Georg Ringer <georg.ringer@gmail.com>
Tested-by: Georg Ringer <georg.ringer@gmail.com>