Take advantage of slots

[bestguy]

We could probably improve many components by adding slot supports for headers, etc vs having to manually nest CardHeader, CardFooter, ToastHeader, alert-heading classes, etc.

[bestguy]

This idea won't be that useful until sveltejs/svelte#1037 is resolved, as currently this currently requires a wrapper html element like a div, etc:

<Card>
  <div slot="header">My Header</div>
  ...

Which doesn't seem any better than what we currently support:

<Card>
  <CardHeader>My Header</CardHeader>
  ...

[Maze-fr]

sveltejs/svelte#1037 has been closed one year ago.