detect whether a file can be validly imported in native node esm context

[danielroe]

Proposed shape:

export async function isValidNativeESM (code: string, id: string): Promise<boolean> {}

Would be useful (elsewhere) to determine whether to inline a given file or whether we can treat it as an external.

[pi0]

Considering it is an async function, should we move id to first and make code optional? Some patterns can be quickly checked without even reading the code like .esm.js files and .json (at the moment)