To be set to false by eglfs and similar platforms where no real window
management is provided.
When this capability is not set, some of the changes done for
QTBUG-26903 will be disabled, allowing dialogs to show up at their
QDialog-chosen place on platforms where no WM is present and so
windows are never repositioned by the system.
Change-Id: If1dac3cd11f2a856913a51277431fe3ec644b719
Reviewed-by: Gunnar Sletta <gunnar.sletta@digia.com>