Update pointer to current tab when the selected tab changes

This allows requests like dumping the DOM tree to be forwarded to the
correct tab. Otherwise, the event would be forwarded to the most
recently created tab.

BrowserWindow.cpp

@@ -10,6 +10,7 @@
 #include "Settings.h"
 #include "SettingsDialog.h"
 #include "WebView.h"
+#include <AK/TypeCasts.h>
 #include <QAction>
 #include <QDialog>
 #include <QPlainTextEdit>
@@ -190,6 +191,7 @@ BrowserWindow::BrowserWindow()
  QObject::connect(m_tabs_container, &QTabWidget::currentChanged, [this](int index) {
  setWindowTitle(QString("%1 - Ladybird").arg(m_tabs_container->tabText(index)));
  setWindowIcon(m_tabs_container->tabIcon(index));
+ m_current_tab = verify_cast<Tab>(m_tabs_container->widget(index));
  });
  QObject::connect(m_tabs_container, &QTabWidget::tabCloseRequested, this, &BrowserWindow::close_tab);
  QObject::connect(close_current_tab_action, &QAction::triggered, this, &BrowserWindow::close_current_tab);