Don't silently ignore creation of new windows

Currently, attempts to create new windows (via links with
`target="_blank"` or JS `window.open`) for pages within the application
have no effect and are silently ignored.
(Links to pages outside the application trigger the allow-intent
functionality and open in Safari.)

With this PR, the default behaviour will be to open those links in the
**same** Web View (without creating a new window).

This also introduces a preference (`AllowNewWindows`) that allows the
creation of a new UIViewController to present the new page in a new Web
View frame on top of the existing Web View.
**Note:** This new window provides no controls, so it can only be closed
with `window.close()` in JS.

CordovaLib/Classes/Private/Plugins/CDVWebViewEngine/CDVWebViewEngine.m

@@ -174,7 +174,9 @@ - (void)pluginInitialize
         self.CDV_ASSETS_URL = [NSString stringWithFormat:@"%@://%@", scheme, hostname];
     }
 
-    self.uiDelegate = [[CDVWebViewUIDelegate alloc] initWithTitle:[[NSBundle mainBundle] objectForInfoDictionaryKey:@"CFBundleDisplayName"]];
+    CDVWebViewUIDelegate* uiDelegate = [[CDVWebViewUIDelegate alloc] initWithTitle:[[NSBundle mainBundle] objectForInfoDictionaryKey:@"CFBundleDisplayName"]];
+    uiDelegate.allowNewWindows = [settings cordovaBoolSettingForKey:@"AllowNewWindows" defaultValue:NO];
+    self.uiDelegate = uiDelegate;
 
     CDVWebViewWeakScriptMessageHandler *weakScriptMessageHandler = [[CDVWebViewWeakScriptMessageHandler alloc] initWithScriptMessageHandler:self];
 

CordovaLib/Classes/Private/Plugins/CDVWebViewEngine/CDVWebViewUIDelegate.h

@@ -20,8 +20,12 @@
 #import <WebKit/WebKit.h>
 
 @interface CDVWebViewUIDelegate : NSObject <WKUIDelegate>
+{
+    NSMutableArray<UIViewController*>* windows;
+}
 
 @property (nonatomic, copy) NSString* title;
+@property (nonatomic, assign) BOOL allowNewWindows;
 
 - (instancetype)initWithTitle:(NSString*)title;
 

CordovaLib/Classes/Private/Plugins/CDVWebViewEngine/CDVWebViewUIDelegate.m

@@ -26,6 +26,7 @@ - (instancetype)initWithTitle:(NSString*)title
     self = [super init];
     if (self) {
         self.title = title;
+        windows = [[NSMutableArray alloc] init];
     }
 
     return self;
@@ -120,4 +121,43 @@ - (void)      webView:(WKWebView*)webView runJavaScriptTextInputPanelWithPrompt:
     [rootController presentViewController:alert animated:YES completion:nil];
 }
 
+- (WKWebView*) webView:(WKWebView*)webView createWebViewWithConfiguration:(WKWebViewConfiguration*)configuration forNavigationAction:(WKNavigationAction*)navigationAction windowFeatures:(WKWindowFeatures*)windowFeatures
+{
+    if (!navigationAction.targetFrame.isMainFrame) {
+        if (self.allowNewWindows) {
+            WKWebView* v = [[WKWebView alloc] initWithFrame:webView.frame configuration:configuration];
+            v.UIDelegate = webView.UIDelegate;
+            v.navigationDelegate = webView.navigationDelegate;
+
+            UIViewController* vc = [[UIViewController alloc] init];
+            vc.modalPresentationStyle = UIModalPresentationOverCurrentContext;
+            vc.view = v;
+
+            [windows addObject:vc];
+
+            UIViewController* rootController = [UIApplication sharedApplication].delegate.window.rootViewController;
+            [rootController presentViewController:vc animated:YES completion:nil];
+            return v;
+        } else {
+            [webView loadRequest:navigationAction.request];
+        }
+    }
+
+    return nil;
+}
+
+- (void)webViewDidClose:(WKWebView*)webView
+{
+    for (UIViewController* vc in windows) {
+        if (vc.view == webView) {
+            [vc dismissViewControllerAnimated:YES completion:nil];
+            [windows removeObject:vc];
+            break;
+        }
+    }
+
+    // We do not allow closing the primary WebView
+}
+
+
 @end