[TASK] Deprecate ControllerContext::getFlashMessageQueue()

With this patch method getFlashMessageQueue() of ControllerContext
is deprecated and the core avoids using it.

A trigger_error call will be implemented in another patch set
which deprecates the whole ControllerContext object.

Releases: master
Resolves: #93016
Change-Id: I20b47dc26892b4affb1aec8e147169738139241c
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/67044


Tested-by: TYPO3com <noreply@typo3.com>
Tested-by: Benni Mack <benni@typo3.org>
Tested-by: Oliver Bartsch <bo@cedev.de>
Tested-by: Daniel Goerz <daniel.goerz@posteo.de>
Reviewed-by: Benni Mack <benni@typo3.org>
Reviewed-by: Oliver Bartsch <bo@cedev.de>
Reviewed-by: Daniel Goerz <daniel.goerz@posteo.de>