[TASK] Update Fluid dependency to version 2.3.1

Solves three issues:

* Namespace declaration output in templates without sections
* Potential error from unexpected input argument in sanitizePath
* Rendering of new HeaderAssets / FooterAssets sections in
   uncompiled templates.

Adds two Fluid features:

* Namespace detection is now in sync with TYPO3 CMS.
* Escaping modifier `{escaping off}` now supported.

And allows the removal of two custom Fluid integrations
contained in TYPO3 which are now included in Fluid.

Change-Id: Ic9cd73d1d05688139241c81e6a3fb78998fe9407
Resolves: #79847
Resolves: #79811
Releases: master
Reviewed-on: https://review.typo3.org/51711


Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>
Reviewed-by: Benni Mack <benni@typo3.org>
Tested-by: Benni Mack <benni@typo3.org>