Ladybird: Explicitly handle setting the AppKit web view's first viewport

We were relying on TabController setting the web view's initial viewport
in [TabController windowDidResize], which has been triggered when the
Tab is first created. However, it turns out that only happens due to the
toolbar being added to the Tab window, causing a resize event. When the
web view is embedded in a window without a toolbar, this resize event is
not triggered. Therefore, we must set the viewport ourselves when the
web view is added to a window.

Ladybird/AppKit/UI/LadybirdWebView.mm

@@ -907,6 +907,12 @@ static void copy_text_to_clipboard(StringView text)
     [super drawRect:rect];
 }
 
+- (void)viewDidMoveToWindow
+{
+    [super viewDidMoveToWindow];
+    [self handleResize];
+}
+
 - (void)viewDidEndLiveResize
 {
     [super viewDidEndLiveResize];