child_process: add AbortSignal support

[benjamingr]

Support AbortSignal in child_process.execFile.

Bikeshedding:

• I know everywhere else it's called signal and that it's the web platform guidance - but I think we might want to deviate here and call the parameter abortSignal to prevent confusion with OS signals and killSignal. WDYT?

I will follow up with support in the other child_process APIs like fork and spawn.

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