Add debug output for QPlatformSurfaceEvent.

[ChangeLog][QtGui][QPlatformSurfaceEvent] Added event class
QPlatformSurfaceEvent, which is sent to QWindow and QOffscreenSurface
when native surface is created or about to be destroyed.

Task-number: QTBUG-42476
Task-number: QTBUG-42483
Change-Id: If62e2c2a1f2a94fd310bbf7cf22b94c70125ba7a
Reviewed-by: Sean Harmer <sean.harmer@kdab.com>