vm: refactor SourceTextModule

- Removes redundant `instantiate` method
- Refactors `link` to match the spec linking steps more accurately
- Removes URL validation from SourceTextModule specifiers
- DRYs some dynamic import logic

Closes: https://github.com/nodejs/node/issues/29030



Co-Authored-By: Michaël Zasso <targos@protonmail.com>

PR-URL: https://github.com/nodejs/node/pull/29776


Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Michaël Zasso <targos@protonmail.com>
Reviewed-By: Minwoo Jung <minwoo@nodesource.com>