[TASK] Add test extension "test_classic_content"

This change adds a new fixture extension
with a content element with a relation to an
inline table.

Resolves: #104369
Releases: main
Change-Id: I777d5dbdebaad4f278bab2dc2b87ebd92f331515
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/85227


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