[10.x] Add Conditional Sleeps

[bradietilley]

This PR is spun off from #47100 and implements the interface that @nunomaduro suggested:

Sleep::for(1)->second()->unless($task->completed());
// or
Sleep::for(1)->second()->when($task->pending());

It also supports a Closure condition (bool return type)

Sleep::for(1)->second()->unless(fn () => $task->completed());
// or
Sleep::for(1)->second()->when(fn () => $task->pending());

If the Closure support is unwanted then I'll get rid of it 🤷