Limited refactor of node.d.ts and express.d.ts

This refactor allows express requests and responses to have their type
declarations reopened/extended. This requires these types to reside in
internal modules, so they have been moved to one called `Express` in
express.d.ts.

`Express.Response` extends node's `"http".ServerResponse`, but internal
modules cannot access types declared within external modules, so the
types in `"http"` have been moved to an internal module called `NodeJs.Http`
in node.d.ts.

In a similar way, the `"http"` declarations depend on the `"net"` module's
`Socket` interface, so that has also been moved into an internal module
called `NodeJs.Net` in node.d.ts.

This PR has zero impact on existing external module declarations, they have all the same type declarations identically as before. But now several types are additionally available ambiently, eg `NodeJs.Net.Socket`, `NodeJs.Http.Server`, `Express.Request`, `Express.Response`, `Express.Application`.