Accordion: isOpen should be two-way bindable

[steelsojka]

The accordion-group component should be able to be bound 2 ways, since the isOpen state can be modified from inside the component and from outside it. The problem scenario occurs when isOpen is bound from outside the component and the user clicks on the accordion. Internally the state is changes, but the binding has not. The change is not communicated back to the parent component.

Instead of the internal state being modified it should emit through an output named isOpenChange with the new value. This will sync the states.

This will be a breaking change however since, currently, if the user clicks on a group when isOpen is bound they still toggle the open state. This change would only respect the bound value. It would require a 2 way data bind to produce the expected behavior.

[steelsojka]

The other alternative is to at least provide an output with the new state to be able to update the parent component. This would be the easiest and non breaking change.

[CodisRedding]

Is two-way binding of isOpen for the accordion implemented in 3.3.0? I'm using isOpen in the component and it will not collapse a group except for the first time.