module: resolve self-references

Adds the ability to `import` or `require` a package from within its
own source code. This allows tests and examples to be written using
the package name, making them easier to reuse by consumers of the
package.

Assuming the `name` field in `package.json` is set to `my-pkg`, its
test could use `require('my-pkg')` or `import 'my-pkg'` even if
there's no `node_modules/my-pkg` while testing the package itself.

An important difference between this and relative specifiers like
`require('../')` is that self-references use the public interface
of the package as defined in the `exports` field while relative
specifiers don't.

This behavior is guarded by a new experimental flag
(`--experimental-resolve-self`).

PR-URL: https://github.com/nodejs/node/pull/29327


Reviewed-By: Guy Bedford <guybedford@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Michaël Zasso <targos@protonmail.com>