* Use npm package names to load internal deps
This is necessary so that published Astro components work. These components will be built by esinstall and therefore they cannot rely on `_astro_internal`. The fix is to use npm specifiers everywhere.
* Move most of frontend to internal
* Mark astro/internal/markdown.js as external
* Move markdown stuff to its own package
This moves the markdown stuff to its own package so that we can externalize it in the markdown component.
* Add the changeset
