module: refactor ESM loader for adding future synchronous hooks

This lays the foundation for supporting synchronous hooks proposed
in nodejs/loaders#198 for ESM.

- Corrects and adds several JSDoc comments for internal functions
  of the ESM loader, as well as explaining how require() for
  import CJS work in the special resolve/load paths. This doesn't
  consolidate it with import in require(esm) yet due to caching
  differences, which is left as a TODO.
- The moduleProvider passed into ModuleJob is replaced as
  moduleOrModulePromise, we call the translators directly in the
  ESM loader and verify it right after loading for clarity.
- Reuse a few refactored out helpers for require(esm) in
  getModuleJobForRequire().