Add horizontal and vertical flexibility (#200)

Author: li-eweng

Sources/ObjCSupport/LOKFlexibility.swift

@@ -21,4 +21,7 @@ import Foundation
     @objc public static let max = LOKFlexibility(flexibility: .max)
     @objc public static let high = LOKFlexibility(flexibility: .high)
     @objc public static let low = LOKFlexibility(flexibility: .low)
+
+    @objc public static let horizontallyFlexible = LOKFlexibility(flexibility: Flexibility(horizontal: Flexibility.defaultFlex, vertical: Flexibility.inflexibleFlex))
+    @objc public static let verticallyFlexible = LOKFlexibility(flexibility: Flexibility(horizontal: Flexibility.inflexibleFlex, vertical: Flexibility.defaultFlex))
 }