mark scripts as shareable cross-origin

This fixes an issue in Electron where errors were being incorrectly sanitized on their way to window.onerror. e.g.

process.nextTick(() => throw new Error('hi'))
window.onerror = e => console.log(e)

was printing "Script error" instead of "Uncaught Error: hi"

This is due to origin-checking logic in Blink: https://chromium.googlesource.com/chromium/src/+/71.0.3578.123/third_party/blink/renderer/core/execution_context/execution_context.cc#114

cc @joyeecheung who is blame on a lot of this code :)

Checklist

• make -j4 test (UNIX), or vcbuild test (Windows) passes
• tests and/or benchmarks are included
• documentation is changed or added
• commit message follows commit guidelines