Improve widget geometry.

Improve widget geometry.

- Rename posFromMove to posIncludesFrame in Widgets and
  make the handling more fine-grained; try to clean it up
  as soon as the frame margins are known
  in QWidgetPrivate::fixPosIncludesFrame().
- Implement QWidgetPrivate::updateFrameStrut().
- Windows: Handle posIncludesFrame in window creation,
  notify changed geometry after setting window flags.
- XCB: Do not change the window gravity in propagateSizeHint()
  as this causes the window to jump around. Determine
  the gravity in window creation, leave it constant and
  fix the geometry when setting instead.
- Store the normal geometry when maximize/fullscreen
  state change events are received.
- Remove xfails from fixed tests

Task-number: QTBUG-25331
Task-number: QTBUG-24905
Task-number: QTBUG-24294

Change-Id: I89c7229d86aaf88f02247d63915da7905e4a27ea
Reviewed-by: Samuel Rødal <samuel.rodal@nokia.com>