Add support for .centerCenter when using the distribute method

[eonist]

for now its possible to do:

let yAnchors = Constraint.distribute(vertically: views, spacing: 24, offset: .init(x: 24, y: 24))
let xAnchors = views.map { Constraint.anchor($0, to: self, align: .centerX, alignTo: .centerX) }
let anchors: [AnchorConstraint] = Array(zip(xAnchors, yAnchors.map { $0.x }))