Support spawning threads from electron ASAR file

In pull request [226](https://github.com/andywer/threads.js/pull/226) you added code that modifies paths containing the string `.asar` because worker files could only be used if they were not packaged in an ASAR file.

In the meantime, the electron team [added support](https://github.com/electron/electron/pull/33216) for working with workers bundled in ASAR files. However, the patch in [226](https://github.com/andywer/threads.js/pull/226) does not allow us to bundle worker scripts because the path is always rewritten to point to the unpacked directory.

Can we add an option to bypass any modifications to the `scriptPath` argument? Thank you for your time.