added NSLayoutConstraint convenience methods

Sources/Toolbox/Extensions/UIKit/NSLayoutConstraint+Convenience.swift

@@ -0,0 +1,20 @@
+#if canImport(UIKit)
+
+import UIKit
+
+public extension NSLayoutConstraint {
+
+    func priority(_ priority: UILayoutPriority) -> NSLayoutConstraint {
+        let constraint = self
+        constraint.priority = priority
+        return constraint
+    }
+
+    func constant(_ constant: CGFloat) -> NSLayoutConstraint {
+        let constraint = self
+        constraint.constant = constant
+        return constraint
+    }
+}
+
+#endif