Kit: move types from WireGuardKit to WireGuardKitTypes.

This prevents linking against wg-go when 3rd-party application needs to
use the WireGuardKit types from within the main bundle, therefore
prevents wg-go from spinning off Golang threads where not applicable.

Signed-off-by: Andrej Mihajlov <and@mullvad.net>

Sources/WireGuardKitTypes/DNSServer.swift

@@ -0,0 +1,35 @@
+// SPDX-License-Identifier: MIT
+// Copyright © 2018-2021 WireGuard LLC. All Rights Reserved.
+
+import Foundation
+import Network
+
+public struct DNSServer {
+    public let address: IPAddress
+
+    public init(address: IPAddress) {
+        self.address = address
+    }
+}
+
+extension DNSServer: Equatable {
+    public static func == (lhs: DNSServer, rhs: DNSServer) -> Bool {
+        return lhs.address.rawValue == rhs.address.rawValue
+    }
+}
+
+extension DNSServer {
+    public var stringRepresentation: String {
+        return "\(address)"
+    }
+
+    public init?(from addressString: String) {
+        if let addr = IPv4Address(addressString) {
+            address = addr
+        } else if let addr = IPv6Address(addressString) {
+            address = addr
+        } else {
+            return nil
+        }
+    }
+}