Add an isOpenInitially argument to the AuAccordion component

[Windvis]

This adds a new defaultOpen isOpenInitially argument to the AuAccordion component which can be used to display the accordion in the open state from the start.

It also adds Glint support to component (also to the AuToolbar component, since that's one of its dependencies.)

Closes #461

[Windvis]

@aliokan I've used the defaultOpen name since that's how it was described in the issue. I did notice we already have a similar argument for the AuCard component but it's called isOpenInitially. I think it makes sense to make these somewhat consistent?

So we could rename it here, or add support for defaultOpen to the other one as well. (Or just keep it as-is) Any opinions?

[aliokan]

@Windvis Thank for the update! 🙏

As I can see, AuCard isOpenInitially is already use in different places: https://github.com/search?q=org%3Alblod%20isOpenInitially&type=code
In order to avoid breaking changes, I would also use isOpenInitially in the accordion.