qtquick: Fix current tab being current even after removed

Added lots of tests for TabBar.

src/qtquick/views/Stack_qtquick.cpp

@@ -157,6 +157,8 @@ void DockWidgetModel::remove(Controllers::DockWidget *dw)
 {
     QScopedValueRollback<bool> guard(m_removeGuard, true);
     const int row = indexOf(dw);
+    const bool wasCurrent = dw == m_currentDockWidget;
+
     if (row == -1) {
         if (!m_removeGuard) {
             // can happen if there's reentrancy. Some user code reacting
@@ -170,6 +172,13 @@ void DockWidgetModel::remove(Controllers::DockWidget *dw)
         for (const QMetaObject::Connection &conn : connections)
             disconnect(conn);
 
+        if (wasCurrent) {
+            const bool isLast = row == count() - 1;
+            const int newCurrentIndex = isLast ? row - 1 : row + 1;
+            if (newCurrentIndex >= 0)
+                setCurrentIndex(newCurrentIndex);
+        }
+
         beginRemoveRows(QModelIndex(), row, row);
         m_dockWidgets.removeOne(dw);
         endRemoveRows();