FileApiReader: Make stopping faster

On the session switch we are busy waiting for the running async task,
started before by the FileApiReader::endState(). This blocks the main
thread for considerable amount of time. E.g. when switching
between sessions both containing Qt project, it may block
the main thread up to 10 seconds.

Instead, we employ the future synchronizer and move the awaiting
to the shutdown phase.

The next patch is going to limit the awaiting in shutdown phase.

Task-number: QTCREATORBUG-27729
Change-Id: I956ed26edcd699d8a4e2b9309d109963f1d4bb20
Reviewed-by: Cristian Adam <cristian.adam@qt.io>

src/plugins/cmakeprojectmanager/fileapireader.cpp

@@ -11,10 +11,13 @@
 
 #include <coreplugin/messagemanager.h>
 
+#include <extensionsystem/pluginmanager.h>
+
 #include <projectexplorer/projectexplorer.h>
 
 #include <utils/algorithm.h>
 #include <utils/async.h>
+#include <utils/futuresynchronizer.h>
 #include <utils/qtcassert.h>
 #include <utils/temporarydirectory.h>
 
@@ -168,7 +171,7 @@ void FileApiReader::stop()
 
     if (m_future) {
         m_future->cancel();
-        m_future->waitForFinished();
+        ExtensionSystem::PluginManager::futureSynchronizer()->addFuture(*m_future);
     }
     m_future = {};
     m_isParsing = false;