tst_QMenu: Add define QTEST_QPA_MOUSE_HANDLING

Use the clean implementation that does not use QCursor::setPos()
with the exception of macOS, where this causes
submenuTearOffDontClose() to fail.

Change-Id: I95a615c37bcf419ce1ede65b5ed79a5ec0568391
Reviewed-by: Gatis Paeglis <gatis.paeglis@qt.io>

tests/auto/widgets/widgets/qmenu/qmenu.pro

@@ -5,4 +5,6 @@ SOURCES  += tst_qmenu.cpp
 macx:{
     OBJECTIVE_SOURCES += tst_qmenu_mac.mm
     LIBS += -lobjc
+} else {
+    DEFINES += QTEST_QPA_MOUSE_HANDLING
 }