[5.5] Use singleton during Schedule creation to allow "resolving" callbacks

[aik099]

By using singleton vs instance method it's now possible for packages to hook into resolving process of Schedule class. For example adding scheduled events from database would look like this:

// In `boot` method of package Service Provider:
$this->app->resolving(\Illuminate\Console\Scheduling\Schedule::class, function ($schedule) {
  // add schedules here
});

Before similar functionality would require code like this:

// In `boot` method of package Service Provider:
if ($this->app->runningInConsole()) {
  // add schedules here
};

The problem is checking for Console for every request, including Http ones.

[aik099]

Or maybe the Container::instance method can be improved to send resolving and resolved events.

[laurencei]

I dont see what the limitation is with the current implementation? It works perfectly fine - many packages already interact with the scheduler without issue...

[aik099]

The limitation is in fact, that you can't alter class instance bound to container via Container::instance method (Schedule in this case) at resolve time only. But you can do that with classes bound via Container::singleton method.

This results in a need of writing code, like checking if we're in Console or not, just to avoid getting object from container before it's created naturally in the application.

Maybe we should do #20933 (comment) instead.

[aik099]

Ah, and I forgot to mention, that I've removed passing Cache instance to the Schedule class, because it's not using it. I guess it was refactored some time ago to let CacheMutex to get Cache directly.