QTest::QTouchEventSequence: add a sleep before each touch movement

In any code (such as QtQuick Flickable) which calculates velocity as
distance / time, it's unrealistic to simulate instantaneous touchpoint
movements.  So, force a slight delay before each event, so that
the touchpoint can only move very fast, but not infinitely fast.
We use qSleep() rather than qWait() because qWait() has a minimum
qSleep(10), and also processes events.  commit() also conditionally
calls processEvents(), and we don't want to make that unconditional.

Change-Id: I3cee890f8951d7ecb8837a6abe216c5a8e0a6e34
Reviewed-by: Liang Qi <liang.qi@qt.io>

src/testlib/qtesttouch.h

@@ -129,6 +129,7 @@ namespace QTest
         void commit(bool processEvents = true)
         {
             if (!points.isEmpty()) {
+                qSleep(1);
                 if (targetWindow)
                 {
                     qt_handleTouchEvent(targetWindow, device, points.values());