Animate NSLayoutConstraint.constant using signals

[indragiek]

First attempt at implementing #4.

[indragiek]

Should this be named Constraint instead? I named it this way to be consistent with RANView.

[jspahrsummers]

Looks good upon a quick skim. ✨

@indragiek Realistically, I probably won't have a whole lot of time to review every PR on here, but I would love to see the project continue—so please feel free to self-merge, if that's helpful. 🙏

Of course, if you ever specifically want me to chime in, mention me and I'll prioritize it.

[indragiek]

@jspahrsummers Thanks, I'll try my best to keep this going when I have time. I'll see what I can do about putting together some examples as well.

Just a question with regards to what's in this PR: do you think it would be an expected behaviour to have signals bound to constraints even after they have been deactivated (i.e. removed from their view)?

[jspahrsummers]

do you think it would be an expected behaviour to have signals bound to constraints even after they have been deactivated (i.e. removed from their view)?

Yeah, I think so. The binding should remain in effect, even though it won't affect what displays on screen.

Only when the constraint is deallocated should the binding cancel, IMO.

[indragiek]

@jspahrsummers 👍 I'll come up with an addition to the example app for this just to make sure everything works as intended and self merge.