feat!: Add icon button

[alimpens]

Some questions:

• Do we want to offer a disabled variant? An Icon Button usually doesn't have any context / text, which makes a disabled button even worse than usual for a11y. -> Discussed, a disabled Icon Button could be useful for application menu bar type things.
• Is onBackground dark / light the right API? We also use onBackground dark for the Search Bar, which isn't necessarily on a dark background. -> We'll discuss this in a separate ticket
• The Alert component should use the Icon Button as well. I didn't do that in this PR to prevent conflict with this PR
• The component currently differs from the design, because having a default padding is a bit cumbersome in use. This padding is necessary for the SearchField component though, so we don't use IconButton there (yet). Discuss this with design.

[VincentSmedinga]

Nice cleanup in the other components!

[VincentSmedinga]

Do we want to offer a disabled variant? An Icon Button usually doesn't have any context / text, which makes a disabled button even worse than usual for a11y.

We should strongly advise against disabling buttons in general, but I don’t think we can leave them out. I expect some disabled icon buttons in applications, e.g. to add or remove something an item from a set.

Is onBackground dark / light the right API? We also use onBackground dark for the Search Bar, which isn't necessarily on a dark background.

Let‘s explore this separately. If we keep using it, we should make clear which backgrounds are light and which are dark. I’ve left some comments on this with the code as well. We use it in other places; no need to hold back this PR.

The Alert component should use the Icon Button as well. I didn't do that in this PR to prevent conflict with this PR

Yes, I’ll make a task to remember that.

[alimpens]

Do we want to offer a disabled variant? An Icon Button usually doesn't have any context / text, which makes a disabled button even worse than usual for a11y.

We should strongly advise against disabling buttons in general, but I don’t think we can leave them out. I expect some disabled icon buttons in applications, e.g. to add or remove something an item from a set.

Good point, I'll add it!

Is onBackground dark / light the right API? We also use onBackground dark for the Search Bar, which isn't necessarily on a dark background.

Let‘s explore this separately. If we keep using it, we should make clear which backgrounds are light and which are dark. I’ve left some comments on this with the code as well. We use it in other places; no need to hold back this PR.

Agreed, I've made a ticket for this

The Alert component should use the Icon Button as well. I didn't do that in this PR to prevent conflict with this PR

Yes, I’ll make a task to remember that.