[refactor] group the built-in conventions (#80957)
Group all the built-in conventions into `src/client/components/builtin` with the actual same name of the conventions they represent.
e.g.
The default `not-found.js` is `next/dist/client/compoents/builtin/not-found.js`;
The default `global-error.js` is `next/dist/client/compoents/builtin/global-error.js`;
This give us an easier way to track all the builtin conventions. This is also the preparation work for #80961 where we display the builtin conventions in the segment explorer.
