Use built-in CollapsibleView instead of DetailsView

Had a chance to try to use CollapsibleView, something like this

This works well from my point of view - especially as it means the DetailsView code that is part of this contrib project wouldn't need to be maintained any more and could be removed.

This suffers from similar tab index issues found at 🐛 Exceptions thrown when toggling Advanced section of linking form Active and not saving link attributes for images found at 🐛 Link attributes don't save Needs review .

This has been introduced in CKEditor after this module has been created.
I'm glad we don't have to maintain this anymore ;)
Thanks!