This commit adds "ext/node" extension that implementes CommonJS module system.
In the future this extension might be extended to actually contain implementation of
Node compatibility layer in favor of "deno_std/node".
Currently this functionality is not publicly exposed, it is available via "Deno[Deno.internal].require"
namespace and is meant to be used by other functionality to be landed soon.
This is a minimal first pass, things that still don't work:
support for dynamic imports in CJS
conditional exports
