Utils: Hide tooltip if application becomes inactive

Switching to another application with "Alt+Tab" was working fine here -
the tooltip closed as expected. But switching by clicking on another
application window lead to a left over tooltip.

Tested with openbox 3.6 window manager.

Task-number: QTCREATORBUG-13397
Change-Id: Id92f6df3b63256a962591df2912a0819fc777073
Reviewed-by: hjk <hjk@theqtcompany.com>

src/libs/utils/tooltip/tooltip.cpp

@@ -48,6 +48,13 @@ ToolTip::ToolTip() : m_tip(0), m_widget(0)
 {
     connect(&m_showTimer, &QTimer::timeout, this, &ToolTip::hideTipImmediately);
     connect(&m_hideDelayTimer, &QTimer::timeout, this, &ToolTip::hideTipImmediately);
+    connect(static_cast<QGuiApplication *>(QGuiApplication::instance()),
+            &QGuiApplication::applicationStateChanged,
+            [this](Qt::ApplicationState state) {
+                if (state != Qt::ApplicationActive)
+                    hideTipImmediately();
+            }
+    );
 }
 
 ToolTip::~ToolTip()