x11: Fix MouseButtonPress events sent to decoration
ButtonPressEvent::state includes keys and buttons prior to the button press has been generated.
On the other hand, it appears that QMouseEvent::buttons() should include currently pressed buttons, i.e. the button that has been just pressed should be in that bitfield.
This is important for QQuickDeliveryAgent, which checks QMouseEvent::button() and QMouseEvent::buttons() to decide whether to send the button event only to tap handlers or both tap handlers and mouse areas.
Edited by Vlad Zahorodnii