Port KRun to OpenUrlJob

In DolphinMainWindow, since KRun allows running executables by default, use
setRunExecutables(true) so as not to change the behaviour.

Remove the now redundant slotHandleUrlStatFinished, that whole StatJob
logic is now handled by OpenUrlJob.

Bump KF required version to 5.73, since that's where
OpenUrlJob::setShowOpenOrExecuteDialog was introduced.