[8.x] Support calling firstOrNew/Create without parameters

[MasterRO94]

This PR allows using firstOrCreate and firstOrNew without parameters.
Useful for tables with default parameters or where all fields are nullable.

For example:

$user->profile()->firstOrNew();

$settings = Settings::firstOrCreate();

For now, we should explicitly pass an empty array and it looks like something is wrong.

[GrahamCampbell]

@gocanto Can you explain why the 👎, otherwise your feedback can't be used.

[gocanto]

@GrahamCampbell yes, I can. 👯

These methods are really a low-level implementation in my opinion and they should be as strict as possible. This method as it stands right now brings a side effect of creating a new record if a given query did not return values. So, stacking yeat another functionality on top of it will hide the rabbit tail even more.

In spite of I share the idea of convenience, I personally believe this is more an app concern than frameworks. Nevertheless, If it were to stay, I will suggest a separate method more aligned with Laravel fashion. Like, createEmpty or CreateWithDefaults

[MasterRO94]

@gocanto
Eloquent Builder::firstOrNew already have an empty array for $attributes. This PR adds the same behavior for firstOrCreate and HasOneOrMany overrides.

And for now the signature for Builder::firstOrNew and HasOneOrMany::firstOrNew is different.

[GrahamCampbell]

Maybe we should change the other method to be stricter too then?

[MasterRO94]

@GrahamCampbell
I think it's up to a developer to either pass parameters or not, IMO.
For one-to-one relations, it will be a good case to just call firstOrNew/firstOrCreate without params.
For now, I just pass an empty array.

[taylorotwell]

I've definitely had situations where I needed to pass an empty array so I think this is generally OK.

[GrahamCampbell]

I've definitely had situations where I needed to pass an empty array

The discussion was if that should be explicitly done by developer or not.