Fix crash when handling WM_PAINT during COM operations

Fix crash when handling WM_PAINT during COM operations

Synchronous expose corrupts painter state if it is done during existing
paint operation, which can happen e.g. when requesting some value from
dumpcpp generated wrapper inside a slot.

Fixed by implementing support for setting asynchronous expose and
doing expose according to the setting in handleWmPaint().

Task-number: QTBUG-27209
Change-Id: I89b5aa823fda947d26b1a4757f129e7c31ea408b
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@digia.com>