Investigate / implement name based discovery of Semi coupled React Components

This would indeed make the DX drastically better, because right now you need to know all the right places that need to be updated, and there's no validation that tells you you forgot about one.

AFAICT the gathering of the relevant information would either:

• happen in semi_coupled_render_template(), on a per-request basis — but this will mean that AJAX updates may need additional mapping information to be passed to the client
• or happen for everything at once — but in this case, this would likely need to be cached, and hence need cache invalidation. Even if it's just the theme registry, it'd likely still need cache invalidation.

How do you imagine that working, @bnjmnm?

I'm not sure if it covers everything that's imagined in #3, but for what's described in the issue summary there's some prior art in https://github.com/drupal-jsx/starter-react/blob/main/src/index.js#L5. Just using Vite's glob function.

📌 Introduce the `xb_stark` theme that uses the Semi-Coupled theme engine, removes the need for taking over the Twig theme engine for the whole site Active landed, and it removed the --xbxb suffix. Issue summary updated.

But that manually constructed/maintained mapping still should be refactored away.