Open Radar

 
Summary:
Right now if you want to deactivate a constraint in interface builder (and then activate it later in code) you have to use a custom IBInspectable that trampolines the setting through to the actual value. It would be great if this was natively exposed to users in Interface Builder

Steps to Reproduce:
1. Try to set isActive on a NSLayoutConstraint in a storyboard

Expected Results:
There's a dropdown to set this value

Actual Results:
There's no way to set this value without defining a custom IBInspectable

Version:
Xcode 9.0 9A235

Notes:
Here's an example of a working inspectable for this case:

```
public extension NSLayoutConstraint {
    @IBInspectable public var isActivated: Bool {
        get { return self.isActive }
        set { self.isActive = newValue }
    }
}
```