[SECURITY] Encode child node variables in f:asset.css view helper

Variables in child nodes like `<f:asset.css>{value}</f:asset.css>`
were not encoded and allow cross-site scripting. In case values shall
be taken as is, corresponding `f:format.raw` instruction has to be used.

Resolves: #97900
Releases: main, 11.5, 10.4
Change-Id: Id843a41c42bbe1f74cdc4efbc117b24d20026b97
Security-Bulletin: TYPO3-CORE-SA-2022-010
Security-References: CVE-2022-36108
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/75719


Tested-by: Oliver Hader <oliver.hader@typo3.org>
Reviewed-by: Oliver Hader <oliver.hader@typo3.org>