[TASK] Allow s and u tags in default RTE processing

Since most of the HTML tags are already allowed,
it makes no sense to make a difference here. The
tags s for strikethrough and u for underline are
now generally available to all RTE configurations.

Resolves: #99456
Releases: main
Change-Id: Ib1b159e70df67af3c34d81285f34d9f7e8288041
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/77256


Reviewed-by: Jasmina Ließmann <minapokhalo+typo3@gmail.com>
Reviewed-by: Benni Mack <benni@typo3.org>
Tested-by: Jasmina Ließmann <minapokhalo+typo3@gmail.com>
Tested-by: Benni Mack <benni@typo3.org>
Tested-by: core-ci <typo3@b13.com>