[TASK] Deprecate constants TYPO3_MODE and TYPO3_REQUESTTYPE

Final patch to deprecate TYPO3_MODE and TYPO3_REQUESTTYPE
with an excessive changelog file to explain details and
migration for extension developers.

Resolves: #92947
Related: #92948
Related: #92951
Related: #92949
Related: #92952
Related: #92953
Releases: master
Change-Id: Id0570582aa08dd34faea3506d5ef8bc85afdda33
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/66948


Tested-by: Oliver Bartsch <bo@cedev.de>
Tested-by: TYPO3com <noreply@typo3.com>
Tested-by: Daniel Goerz <daniel.goerz@posteo.de>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>
Reviewed-by: Oliver Bartsch <bo@cedev.de>
Reviewed-by: Daniel Goerz <daniel.goerz@posteo.de>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>