UnitTests: Add mockup for Core::ICore::userResourcePath()

Otherwise the unit tests does not linked any more.

Change-Id: I1d756b8bef18d65174a8924a15995cc179af61f3
Reviewed-by: Marco Bubke <marco.bubke@qt.io>

tests/unit/mockup/coreplugin/icore.h

@@ -0,0 +1,10 @@
+#include <QDir>
+
+namespace Core {
+namespace ICore {
+static QString userResourcePath()
+{
+     return QDir::tempPath();
+}
+} // namespace ICore
+} // namespace Core