Fix Focus problem with QX11EmbedWidget

Since QX11EmbedWidget can be included in another Qt application which
has QX11EmbedContainer, QX11EmbedWidget should be activated at first.

Task-number: QTBUG-3617
Change-Id: I23e12f6c3ed9f7bd4a3ac0d0237bf7382db14ee2
Reviewed-by: Shawn Rutledge <[email protected]>

Author: luyikei

src/gui/kernel/qx11embed_x11.cpp

@@ -492,6 +492,9 @@ QX11EmbedWidget::QX11EmbedWidget(QWidget *parent)
     setSizePolicy(QSizePolicy::Expanding, QSizePolicy::Expanding);
     QApplication::instance()->installEventFilter(this);
 
+    // Focus itself at first.
+    qApp->setActiveWindow(this);
+
 #ifdef QX11EMBED_DEBUG
     qDebug() << "QX11EmbedWidget::QX11EmbedWidget: constructed client"
              << (void *)this << "with winId" << winId();