Export new Web Components #774

As part of #769, we've created a bunch of new components under "design-system" and "primitives". However, these are only used internally from now. The idea was that they could be reused in other projects as well, but we still have to decide how we want to export them, and how we migrate from the previous set of components (for example, there was also a "button" component before).

In particular, the "primitives" components are supposed to be usable in any Solid project, even without using solid-ui, so they're probably going to be released in a different package. But we still haven't decided which one.