Misc Cleanup: JAWTWindow: Reusing visible in HIERARCHY listener; Remove obsolete 'getPrivateGraphicsConfiguration()'
Fix GLDrawableHelper.resizeOffscreenDrawable(..): Do nothing if !drawable.isRealized() - similar to it's recreateDrawable() and test only _after_ having the surface lock!

Only after the surface lock we are thread safe.

In case drawable has been pulled, do nothing ..
Bug 937 - JAWTWindow: Unsatisfying Visibility Computation

Simplify JAWTComponentListener's HierarchyListener:
  - Don't interfere w/ Component's visibility anymore!
    This shall reduce sideeffects.
    Utilize 'isShowing' in each Component specialization, i.e. GLCanvas.

  - On SHOWING_CHANGED if a parent caused a change
    of the tracked components showing state,
    propagate it to the offscreen-layer!

  - Remove all other complicated states!

GLCanvas, GLJPanel:
  - Instead of 'isVisible()' use 'showing state',
    since only the 'showing state' reflects 'true' visibility
    throughout the hierarchy.

  - Add HierarchyListener and track volatile showing state
    to be used instead of 'isVisible'.
    Using a cached showing state is more efficient
    than quering 'isShowing()' all the time!

NewtCanvasAWT:
  - Use 'isShowing()' instead of 'isVisible(), see above
AWTParentWindowAdapter/AWTRobotUtil: Use 'isShowing()' instead of 'isVisible()' determining actual on-screen showing state

See commit 071bdd6ce9f8c41ccecdbf8bc74f276ccd7ff651
DefaultEDTUtil: At EDT finish, notify all task-waiter to avoid deadlock at error / Add test method 'invokeAndWaitError(..)'