[ base ] Add getThreadId

[Matthew-Mosior]

Description

This PR adds the getThreadId function to System.Concurrency (chez backend).

Should this change go in the CHANGELOG?

• If this is a fix, user-facing change, a compiler change, or a new paper
  implementation, I have updated CHANGELOG_NEXT.md (and potentially also
  CONTRIBUTORS.md).

[Matthew-Mosior]

I think channels008 is the issue here on the windows-bootstrap-chez workflow.

[Matthew-Mosior]

Should be ready for review.

[cypheon]

Should this function maybe rather return a value of type PrimIO.ThreadID (the same type as returned by fork when creating a new thread) instead of Int?

[Matthew-Mosior]

Should this function maybe rather return a value of type PrimIO.ThreadID (the same type as returned by fork when creating a new thread) instead of Int?

Hmm, it appears there isn't a way to show a ThreadID, as its an opaque thread object in scheme.

Is this what we want here? I think it would be great to be able to somehow show and/or cast this value (to be able to create hashes off of, etc.). Thinking about use and testing here.