Delay renderWindow with a timer

Add an exhaust delay to QSGGuiThreadRenderLoop. Some updates
may be done with posted events, and maybeUpdate event competed
with those, leading to partial updates and frames drawn twice.

Change-Id: I532bff692c597eeba5bbd6def89ae68c80fdd69b
Done-with: Mikko Harju <mikko.harju@jollamobile.com>
Reviewed-by: Gunnar Sletta <gunnar.sletta@digia.com>
TextInput: call fixup() when appropriate

[ChangeLog][QtQuick] Fixed TextInput to call fixup() on its validator
when being accepted or losing focus, and the validator reports that the
input is in "intermediate" state ie. the input should be fixed up.

Task-number: QTBUG-35128
Change-Id: I4b15406c584a9647bcf892badfaf6d845868fbf1
Reviewed-by: Liang Qi <liang.qi@digia.com>