Restructure Web Components

After some team discussions, we've decided that we won't differentiate web components by "primitives" or "design system" anymore. Instead, they will all be plain web components exported by the solid-ui package; some more reusable or ambitious than others.

We can still categorize them in some way for code organization or documentation, but they won't be separated in a different package or namespace (they'll all have the <solid-ui prefix).