The new test tst_QTouchEvent::touchOnMultipleTouchscreens()
needs the touchpoint IDs to be predictable, but another test currently
has a QEXPECT_FAIL; without release events, g_pointIdMap continued to
hold the touchpoints that were there when the test failed. So it's
necessary to add QWindowSystemInterfacePrivate::clearPointIdMap()
to be able to call it in the test cleanup function.
Fixes: QTBUG-73830
Change-Id: Ia6a70d028be95cd2b6676db6363ec408c0b116bc
Reviewed-by: Jan Arve Sæther <jan-arve.saether@qt.io>