TaskTree: Add synchronous invocation (Tasking::Sync)

Make it possible to mix synchronous and asynchronous calls
inside task tree.

Basically, it's a shortcut for:

bool syncMethod();
Group {
    OnGroupSetup([syncMethod] { return syncMethod()
                                ? TaskAction::StopWithDone
                                : TaskAction::StopWithError; })
}

Please note: similarly to Group, Sync isn't counted as a task
inside taskCount() and doesn't emit TaskTree::progressValueChanged()
when finished. It's being considered as a simple handler
that doesn't last long and shouldn't block the GUI thread.
Otherwise, use AsyncTask instead.

Change-Id: If71c5da2f9b202a69c41a555cc93d314476952f4
Reviewed-by: Eike Ziller <eike.ziller@qt.io>

src/libs/utils/tasktree.h

@@ -244,6 +244,16 @@ public:
     OnGroupError(const GroupEndHandler &handler) : TaskItem({{}, {}, handler}) {}
 };
 
+// Synchronous invocation. Similarly to Group - isn't counted as a task inside taskCount()
+class QTCREATOR_UTILS_EXPORT Sync : public Group
+{
+public:
+    using SynchronousMethod = std::function<bool()>;
+    Sync(const SynchronousMethod &sync)
+        : Group({OnGroupSetup([sync] { return sync() ? TaskAction::StopWithDone
+                                                     : TaskAction::StopWithError; })}) {}
+};
+
 QTCREATOR_UTILS_EXPORT extern ParallelLimit sequential;
 QTCREATOR_UTILS_EXPORT extern ParallelLimit parallel;
 QTCREATOR_UTILS_EXPORT extern Workflow stopOnError;