Container 45237: Fix Block Header Keyboard Access

[matheuszych]

See: https://mantis.ilias.de/view.php?id=45237

Expandable container block headers were not keyboard accessible. Collapsible item group headers can now receive focus, toggle with Enter or Space, keep aria-expanded in sync, and use standard ILIAS focus styling.

/cc @oliversamoila @thojou

[oliversamoila]

Context from the Mantis ticket:

Hello everyone.

I’ve been getting an increasing number of questions about whether a solution can still be found for the »»current«« implementation.
We have to accept that we won’t be seeing a migration of the repository to ILIAS 12. This means, conversely, that if we don’t address the issue, it will carry over into at least releases 10, 11 and 12.

My colleague @matheuszych has kindly created a PR for this. Many thanks!
This can be found under #12066 .

I’d be grateful if @Annett7811 could provide some feedback on this (feel free to do so in the PR as well).
I’d then pass it on to @alex40724 for a review and integration, as the changes aren’t located in the ‘ItemGroup’ directory but in ‘Container’.

Many thanks to everyone involved.

[Annett7811]

Hello @matheuszych!

From an accessibility standpoint, this looks good. The object block can now be opened using the keyboard when it is closed. Thank you very much for your work and for fixing this!

Best regards
@Annett7811

[alex40724]

Thanks for the PR. This looks good from my side. CSS needs to be checked by @BettyFromHH

@matheuszych I assigned you. If all reviews are positive you can merge this.