UIKitBackend: Implement openURL action, kind of support colorScheme(_:)

Only supports colorScheme(_:) for text at the moment, and doesn't
dynamically react when the system color scheme changes.

Author: stackotter

Sources/UIKitBackend/ColorScheme+UIUserInterfaceStyle.swift

@@ -0,0 +1,13 @@
+import SwiftCrossUI
+import UIKit
+
+extension ColorScheme {
+    var userInterfaceStyle: UIUserInterfaceStyle {
+        switch self {
+            case .light:
+                return .light
+            case .dark:
+                return .dark
+        }
+    }
+}

Sources/UIKitBackend/UIKitBackend+Passive.swift

@@ -41,8 +41,11 @@ extension UIKitBackend {
         environment: EnvironmentValues
     ) {
         let wrapper = textView as! WrapperWidget<UILabel>
+        wrapper.child.overrideUserInterfaceStyle = environment.colorScheme.userInterfaceStyle
         wrapper.child.attributedText = UIKitBackend.attributedString(
-            text: content, environment: environment)
+            text: content,
+            environment: environment
+        )
     }
 
     public func size(

Sources/UIKitBackend/UIKitBackend.swift

@@ -111,6 +111,10 @@ public final class UIKitBackend: AppBackend {
 
     public func show(widget: Widget) {
     }
+
+    public func openExternalURL(_ url: URL) throws {
+        UIApplication.shared.open(url)
+    }
 }
 
 extension App {