[!!!][FEATURE] Add PSR-14 events for the BackendController

This introduces two new events to interact with the backend
controller page generation process. They mirror and replace
the renderPreProcess and renderPostProcess hooks, which are removed.

The vestigial constructorPostProcess hook is also removed entirely.

Resolves: #97451
Releases: main
Change-Id: I58bccf341b478eedc87c9a9dd81fac788bba0a91
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/74797


Tested-by: Stefan Bürk <stefan@buerk.tech>
Tested-by: core-ci <typo3@b13.com>
Tested-by: Benni Mack <benni@typo3.org>
Reviewed-by: Stefan Bürk <stefan@buerk.tech>
Reviewed-by: Benni Mack <benni@typo3.org>