Feature: Tab panel

[bjarnef]

Currently there's a <uui-tabs> component and also a <uui-tab-group> although list isn't listed in the readme here: https://github.com/umbraco/Umbraco.UI

However when it comes to accessibility I think it is missing a <uui-tab-panel> component as well, which is connected to the specific tab.
For example: https://shoelace.style/components/tab-panel

[bjarnef]

@iOvergaard not sure how the tabel panel are implemented with tabs in the new backoffice, but it think <uui-tab-panel> inside <uui-tab-group> would make it simpler to connect each tab to its panel and control the necessary aria attributes, e.g. aria-selected, aria-controls, aria-labelledby, aria-expanded etc.

[bjarnef]

I started a PR here: #600

[iOvergaard]

Sounds good, @bjarnef, and I agree. Let's build it.