Is your feature request related to a problem? Please describe.
I want to be able to add classes to slots so that i can style them directly.

Describe the solution you'd like

App.svelte

<MyComponent>
    <ul slot="list">
       ...
    </ul>
</MyComponent>

MyComponent.svelte

<slot name="list" class="my-list-style">
   <p>No items found</p>
</slot>

Describe alternatives you've considered
This alternative works, but i still can't style the ul in my example correctly and it feels like it renders the fallback slot functionality useless.

{#if list.length}
<div class="my-list-style">
   <slot name="list" />
</div>
{:else}
<p>No items found</p>
{/if}

How important is this feature to you?
There are work arounds, but nothing clean. I just feel like this should be functionality that should be part of the slot feature.