Infer superview & return (constraints, views)

[BrianKenny]

This PS does 2 things. It lets regular view nodes opt into the inferred superview logic that's currently used for ghost views, in the case where they don't have a superview when constraints are created. This often gets rid of the need to ad subviews explicitly. Second, all the capture list operators go from returning just the constraints to returning a tuple of the constraints and the views. I've been converting all my spacerview code to mortarVFL, and almost every case we have something like

let theViews = [v1, v2, .........]
self.view |+| theViews
self.view |^^ v1 | v2 | .......
theViews.m_...

//Which now becomes something like

let theViews = (self.view |^^ v1 | v2 ........).views
theViews.m_....

It only saves 2 lines, but one of those is re-writing the array in a different form, which is tedious and error prone.