Make integer multiplication bounds-consistent

[ThatsJustUnlucky]

This implements bounds-consistent propagation for the integer multiplication constraint a * b = c.

The write-up is attached below.

multiplication-writeup.pdf

[maartenflippo]

This a great effort, thank you for the contribution. A few comments:

1. Why is this a draft PR? Do you still expect to work on this, or is it ready for review?
2. Could you convert the write-up to markdown and post it as the PR body? That way, if we merge the PR, the write-up becomes the commit body. It provides good information for the future.
3. I have not looked at the code yet, but from the write-up, I see you iterate over domains to find supports. This is a slightly problematic behavior, as this propagator can be implemented in $O(1)$ time. See section 2.3 of this paper.

[EmirDe]

Just to add some context, this is the potential "honours" student, I have yet to review and discuss the PR with the student (I hope to have time next week).