[BUGFIX] Respect `data-content` for modals again

With the upgrade to Bootstrap 5, modals unintentionally don't support
the `data-content` attribute anymore as this was automatically migrated
to the namespaced variant `data-bs-content`. While this is technically
correct for Bootstrap 5, Core still needs to support the old variant as
documented.

Resolves: #98067
Releases: main, 12.4, 11.5
Change-Id: I544cbd779c808727c472575654adca3dc4c91197
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/79974


Tested-by: Oliver Bartsch <bo@cedev.de>
Tested-by: core-ci <typo3@b13.com>
Reviewed-by: Oliver Bartsch <bo@cedev.de>