Fix SWTEDTUtil regression caused by dec4b02fe4b93028c85de6a56b6af79601042d6e, ensuring EDT is running for reused Display instances.

Refine EDTUtil semantics of:
  - reset()
  - waitUntilStopped()

AWTEDTUtil/SWTEDTUtil: Properly signal !running when shutdown

SWTEDTUtil: Take SWT isDisposed() into account.