Fix tst_qquicktextinput::copyAndPaste() for asynchronous clipboard notification.

Change qtbase 6a61a00ddb21e79412e82069dfef50192bfd724d for Windows uses
new clipboard notification API that results in asynchronous clipboard
notifications.

Task-number: QTBUG-39145
Task-number: QTBUG-38670
Task-number: QTBUG-33492
Change-Id: I0de78ecba5c67bf6a66f07e59312667f6ce6bf88
Reviewed-by: J-P Nurmi <jpnurmi@digia.com>