UI/Qt: Ensure we don't add the same zoom shortcut key more than once

On my system `QKeySequence::StandardKey::ZoomIn` includes both `Ctrl++`
and `Ctrl+=`, so explicitly adding the secondary `Ctrl+=` shortcut
ourselves results in an ambiguous shortcut error message being shown.

According to the Qt documentation the key bindings returned by
`QKeySequence::StandardKey::*` are platform specific, so we may still
need to add the secondary shortcut on some systems. Therefore, we now
check whether our secondary shortcut is already in the shortcut list
before adding it.

Ladybird/Qt/BrowserWindow.cpp

@@ -186,7 +186,10 @@ BrowserWindow::BrowserWindow(Vector<URL::URL> const& initial_urls, WebView::Cook
     auto* zoom_in_action = new QAction("Zoom &In", this);
     zoom_in_action->setIcon(load_icon_from_uri("resource://icons/16x16/zoom-in.png"sv));
     auto zoom_in_shortcuts = QKeySequence::keyBindings(QKeySequence::StandardKey::ZoomIn);
-    zoom_in_shortcuts.append(QKeySequence(Qt::CTRL | Qt::Key_Equal));
+    auto secondary_zoom_shortcut = QKeySequence(Qt::CTRL | Qt::Key_Equal);
+    if (!zoom_in_shortcuts.contains(secondary_zoom_shortcut))
+        zoom_in_shortcuts.append(AK::move(secondary_zoom_shortcut));
+
     zoom_in_action->setShortcuts(zoom_in_shortcuts);
     m_zoom_menu->addAction(zoom_in_action);
     QObject::connect(zoom_in_action, &QAction::triggered, this, &BrowserWindow::zoom_in);