[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>

Build/Sources/TypeScript/backend/modal.ts

@@ -486,7 +486,7 @@ class Modal {
   private initializeMarkupTrigger(theDocument: Document): void {
     const modalTrigger = (evt: Event, triggerElement: HTMLElement): void => {
       evt.preventDefault();
-      const content = triggerElement.dataset.bsContent || TYPO3.lang['message.confirmation'] || 'Are you sure?';
+      const content = triggerElement.dataset.bsContent || triggerElement.dataset.content || TYPO3.lang['message.confirmation'] || 'Are you sure?';
       let severity = SeverityEnum.info;
       if (triggerElement.dataset.severity in SeverityEnum) {
         const severityKey = triggerElement.dataset.severity as keyof typeof SeverityEnum;