TaskTree: Introduce Timeout task

By default, when finished, it returns success.
In order to convert it into failing task,
enclose it inside a Group with finishAllAndError.

Reuse it in tasking tests.

Task-number: QTCREATORBUG-28741
Change-Id: Ic81203203e0b139d4f9bfd553279ecb01cd303f4
Reviewed-by: Marcus Tillmanns <marcus.tillmanns@qt.io>
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>

src/libs/solutions/tasking/tasktree.cpp

@@ -1848,4 +1848,14 @@ void TaskTreeTaskAdapter::start()
     task()->start();
 }
 
+TimeoutTaskAdapter::TimeoutTaskAdapter()
+{
+    *task() = std::chrono::milliseconds::zero();
+}
+
+void TimeoutTaskAdapter::start()
+{
+    QTimer::singleShot(*task(), this, [this] { emit done(true); });
+}
+
 } // namespace Tasking