Support custom Link and Image components for meta frameworks

[endigo9740]

There are several meta frameworks that make use of custom components for handling Links (for routing) and Images (for CDNs and optimization). Any Skeleton component that supports links or images may need to have this exposed to allow inserting these special components. Implementation will likely vary between Svelte/React/other frameworks.

This includes, but may not be limited to:

• Svelte's @sveltejs/enhanced-img
• Next.js's Image and Link components
• Astro's Image component

Some "hybrid" frameworks may have this as well, such as Inertia for PHP/Laravel.

[endigo9740]

So far this is happening indirectly through support of features and child slots. Let's continue forward with this pattern.