ProjectExplorer: Fix potential race condition

When using BuildStep::runImpl() it was possible for the async part
to still be running while the BuildStep is already deleted.

This change returns the Future so that users can wait for it to finish.

Change-Id: I27c0fc8741c59851c5ab8f5cb858fbcda923c14d
Reviewed-by: Jarek Kobus <jaroslaw.kobus@qt.io>
Reviewed-by: <github-actions-qt-creator@cristianadam.eu>

src/plugins/android/androiddeployqtstep.h

@@ -12,6 +12,7 @@
 
 #include <utils/commandline.h>
 #include <utils/environment.h>
+#include <utils/futuresynchronizer.h>
 
 namespace Utils { class QtcProcess; }
 
@@ -91,6 +92,8 @@ private:
     Utils::FilePath m_workingDirectory;
     Utils::Environment m_environment;
     AndroidDeviceInfo m_deviceInfo;
+
+    Utils::FutureSynchronizer m_synchronizer;
 };
 
 }