feat: support for statically added closure global scopes

[boumanb]

Adds support for statically added Closure global scopes.

Example:

protected static function boot()
{
    parent::boot();

    static::addGlobalScope('order', function ($builder) {
        $builder->orderBy('first_name')->orderBy('last_name');
    });
}

This would throw a Instantiation of 'Closure' is not allowed before.

[luisdalmolin]

@boumanb Thank you, this sounds great. Would you mind adding a test covering this use case? Then I'll merge and tag this change.

[boumanb]

@boumanb Thank you, this sounds great. Would you mind adding a test covering this use case? Then I'll merge and tag this change.

Done. Thanks.