Is your feature request related to a problem? Please describe.
There is no proper way to forward slots other than for them to be wrapped in a parent element.

Describe the solution you'd like
The slot prop to be able to be added to slot elements.

<Component>
  <slot slot="inherited" name="forwarded" />
</Component>

Where the slot inherited is forwarded as forwarded to the component that consumes this one.

Describe alternatives you've considered
Wrapping the slot in a div element, causes problems with flexbox and performance.

How important is this feature to you?
3/5. not too important but very useful to have.

Additional context
https://svelte.dev/repl/5acc582e28f04d06aff5f3b861e7537f?version=3.29.0