[TASK] Deprecate various hooks related to TypoScriptFrontendController

PSR-15 and Request/Response handling has been proven to be a
worthy replacement for most logic related for outputting content
in the TYPO3 Frontend.

In order to thin out TSFE in future TYPO3 versions, various hooks have
been deprecated as they can also be used with proper PSR-15 middlewares.

* $GLOBALS['TYPO3_CONF_VARS']['SC_OPTIONS']['tslib/class.tslib_fe.php']['pageIndexing']
* $GLOBALS['TYPO3_CONF_VARS']['SC_OPTIONS']['tslib/class.tslib_fe.php']['isOutputting']
* $GLOBALS['TYPO3_CONF_VARS']['SC_OPTIONS']['tslib/class.tslib_fe.php']['tslib_fe-contentStrReplace']
* $GLOBALS['TYPO3_CONF_VARS']['SC_OPTIONS']['tslib/class.tslib_fe.php']['contentPostProc-output']

The following methods are marked as deprecated as well:
* $TSFE->isOutputting()
* $TSFE->processContentForOutput()

Resolves: #91012
Releases: master
Change-Id: I455f110f7f3e774de9d8ccd4adfcbd1ed5538cec
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/64118


Tested-by: Georg Ringer <georg.ringer@gmail.com>
Tested-by: Josef Glatz <josefglatz@gmail.com>
Tested-by: TYPO3com <noreply@typo3.com>
Tested-by: Benni Mack <benni@typo3.org>
Reviewed-by: Georg Ringer <georg.ringer@gmail.com>
Reviewed-by: Josef Glatz <josefglatz@gmail.com>
Reviewed-by: Benni Mack <benni@typo3.org>