[10.x] createMany & createManyQuietly add count argument

[JHWelch]

Adds the ability to pass an int to the createMany and createManyQuietly functions on Model Factories to create that number of models..

// Before: $users = User::factory()->createMany([[], [], []]);
$users = User::factory()->createMany(3);

$this->assertCount(3, $users);
$this->assertInstanceOf(Eloquent\Collection::class, $users);

createMany is useful for static typing because it always returns an Eloquent Collection, similar to how the createOne method always returns a single model. However currently you must pass an array of argument arrays. This change allows you to pass a count of the total records you want generated instead.

I could look at doing this with the normal create mechanism and confirming the type, but this seemed the most straight forward approach.