Convert classes on wrapper attributes into arrays

Hi,

Encountered a fatal error with 🐛 Fatal error when using the Diff module Fixed yesterday due to class attribute not being an array.

I will secure contrib theme but it would be good that this issue is fixed.

Thanks for the patches.

Converted to an MR and rebased, this conflicted pretty heavily with a change that converted to short array syntax.

I slightly changed some of the ternary conditions, so that the fallback is an empty array and not an array with NULL.

Looks like 🐛 Define CSS classes as an array Fixed missed some of these. Rebasing and running fresh pipelines.

Automatically closed - issue fixed for 2 weeks with no activity.