Invalid aria-activedescendant attribute set on carousel

[twelsh920]

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Bug description:

The ngb-carousel sets the aria-activedescendant attribute to an invalid id (uses activeId variable when should be using 'slide-'+activeId to match the actual tabpanel ids)

Link to minimally-working StackBlitz that reproduces the issue:

Run a chromium Lighthouse accessibility audit on any page with an ngb-carousel and ngbSlide to see warning

Can even just run audit on https://ng-bootstrap.github.io/#/components/carousel/examples to see the warnings

Confirmed that prepending "slide-" to value of aria-activedescendant resolves the issue.

You can fork a StackBlitz from one of our demos and use it as a starting point.

Please note that we can not act on bug reports without a minimal reproduction scenario in a StackBlitz. Here is why:
https://github.com/ng-bootstrap/ng-bootstrap#you-think-youve-found-a-bug

Versions of Angular, ng-bootstrap and Bootstrap:

Angular: 11

ng-bootstrap: 9.0.2

Bootstrap: 4.5.0