ProjectExplorer: Move ProcessHandle to Utils for further re-use

Also, use qint64 instead of quint64, as this is what Qt uses.

Keep 0 for invalid PIDs, even if arguably -1 would be better,
but Qt uses 0, too.

Don't move 'toString', instead inline it into the only
caller, keeping translations intact.

Task-number: QTCREATORBUG-17596
Change-Id: Ie9411ea1d2031a5ab0a99bcb3ff48ee430afe254
Reviewed-by: Tobias Hunger <tobias.hunger@qt.io>

src/plugins/debugger/debuggerengine.cpp

@@ -63,6 +63,7 @@
 
 #include <utils/fileinprojectfinder.h>
 #include <utils/macroexpander.h>
+#include <utils/processhandle.h>
 #include <utils/qtcassert.h>
 #include <utils/savedaction.h>
 
@@ -80,6 +81,7 @@ using namespace Core;
 using namespace Debugger::Internal;
 using namespace ProjectExplorer;
 using namespace TextEditor;
+using namespace Utils;
 
 //#define WITH_BENCHMARK
 #ifdef WITH_BENCHMARK