(ios): allow to set "preferredContentMode" (#688)

PreferredContentMode can now be set with preference config. Since iPadOS came out iPads get a desktop Safari useragent by default.

see #687 

Co-authored-by: Tim Brust <github@timbrust.de>

src/ios/CDVWKInAppBrowser.m

@@ -757,6 +757,15 @@ BOOL isExiting = FALSE;
         configuration.mediaPlaybackRequiresUserAction = _browserOptions.mediaplaybackrequiresuseraction;
     }
     
+    if (@available(iOS 13.0, *)) {
+        NSString *contentMode = [self settingForKey:@"PreferredContentMode"];
+        if ([contentMode isEqual: @"mobile"]) {
+            configuration.defaultWebpagePreferences.preferredContentMode = WKContentModeMobile;
+        } else if ([contentMode  isEqual: @"desktop"]) {
+            configuration.defaultWebpagePreferences.preferredContentMode = WKContentModeDesktop;
+        }
+        
+    }
     
 
     self.webView = [[WKWebView alloc] initWithFrame:webViewBounds configuration:configuration];