[webview_flutter_wkwebview] Add support for javaScriptCanOpenWindowsAutomatically

[fummicc1]

This PR adds support for WKPreferences.javaScriptCanOpenWindowsAutomatically to allow JavaScript's window.open() to work without user interaction on iOS and macOS.

Changes

• Added javaScriptCanOpenWindowsAutomatically parameter to WebKitWebViewControllerCreationParams
• Exposed setJavaScriptCanOpenWindowsAutomatically method via Pigeon API
• The setting is applied when setJavaScriptMode is called

Usage

final controller = WebKitWebViewController(
  WebKitWebViewControllerCreationParams(
    javaScriptCanOpenWindowsAutomatically: true,
  ),
)
  ..setJavaScriptMode(JavaScriptMode.unrestricted)
  ..loadRequest(Uri.parse('https://example.com'));

Proof

I checked this behavior with a demo in this PR

The screen capture below shows that 5 seconds after pressing the button, the WebView shows the destination only if javaScriptCanOpenWindowsAutomatically is true.

Screen.Recording.2025-12-16.at.3.40.48.mp4

[gemini-code-assist]

Code Review

This pull request adds support for javaScriptCanOpenWindowsAutomatically to allow JavaScript's window.open() to work without user interaction on iOS and macOS. The changes are well-implemented across Dart and Swift files, including the necessary Pigeon interface updates, native implementation, and tests. I have a couple of suggestions to improve the code. One is to refactor the setJavaScriptMode method in webkit_webview_controller.dart to reduce code duplication, which will enhance maintainability. The other is a minor improvement in the new Swift test to ensure better error reporting.