[Custom Components] Support Named Slots in svelte

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Is your feature request related to a problem? Please describe.
Custom components can only use Default Slot in svelte currently, therefore it cannot provide more customized layout configurations for users. I'm wondering if gradio can provide a component like gr.Slot to support Named Slot.

Describe the solution you'd like
This is a sample to use gr.Slot: app.py

with CustomComponent():
    # default slot
    gr.Button()
    # named slot
    with gr.Slot(name="extra"):
        gr.Button()

custom_components/Index.svelte

<div><slot/></div>
<div><slot name="extra"/></div>

Additional context
Add any other context or screenshots about the feature request here.