[#137] Make ui_tabs accessible

[hannahbit]

Fixes the ui_tabs not following accessibility guidelines.

See issue: #137

[hannahbit]

The gap is now slightly smaller. This is because the default bitstyles does not have a u-gap-s2. The closest available options are u-gap-s3 (which I chose) and u-gap-m. Which would be bigger.
I thought having a little smaller gap might be fine? WDYT?

before	now

[andreasknoepfle]

I think this would be just needing a CHANGELOG entry and then be good to go.

I thought having a little smaller gap might be fine? WDYT?

Since one can always set another gap class and overwrite the default one with it it should be fine imho.

[klappradla]

The code and the generated docs look fine 👍

What does not work for me is the demo application though. Is it known to be broken or is this a new thing?

[hannahbit]

What does not work for me is the demo application though. Is it known to be broken or is this a new thing?

It's the same on main for me and unrelated to the changes made in here. The demo needing a rework is already a known issue.

[hannahbit]

@andreasknoepfle @klappradla Thanks for the reviews 🧡

I updated the changelog. Can you take another look?

[klappradla]

Maybe worth mentioning what you wrote in the issue

replace the <ul> with a <div role="tablist">

[klappradla]

Ready for 🌊 I'd say.