[TASK] Deprecate two FlexFormTools methods

Methods FlexFormTools->getArrayValueByPath() and
FlexFormTools->setArrayValueByPath() have well test
covered counterparts in ArrayUtility since v7.

Usages can be adapted easily and the outdated
implementations can be deprecated.

Change-Id: Ieb40369c883b95f6c7cc398cfdab3a9a08054b8f
Resolves: #95254
Releases: master
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/71112


Tested-by: core-ci <typo3@b13.com>
Tested-by: Benni Mack <benni@typo3.org>
Tested-by: Jochen <rothjochen@gmail.com>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>
Reviewed-by: Benni Mack <benni@typo3.org>
Reviewed-by: Jochen <rothjochen@gmail.com>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>