Native context menu shows every second time

Reproduce:

1. start qtdeclarative/tests/manual/quickcontrols/menus
2. set popupType to "Native"
3. Right-click in the area above the "Context menu" to show the context menu
4. Close it by left-clicking outside
5. GOTO 3

For native context menus, calls to Popup.open() will be blocking, which is the distinguishing factor from using e.g Popup.Window or Popup.Item. And since a press on the button in the menus test opens a native blocking context menu, the corresponding mouse release will not be sent to Qt (but to the native context menu).

Some observations:
You will see that on every second right-click the context menu doesn't show up. It might be because:

1. Right button is pressed: right-press is sent to the main window, then brings up a new context menu Window
2. Right button is released: When right-release is sent, it is sent to the new context menu Window is under the mouse
3. context menu closes
4. Right button is pressed: DA of the main window is still thinking that right mouse button is pressed, so a subsequent right mouse button press does nothing
5. Right button is released: right-release is processed by the DA and is reset back to "no buttons pressed"
6. Right button is pressed: DA state is now that no buttons are pressed. It will therefore change state to right-button-pressed and consequently open the Context menu