[9.x] Improve signature for HasFactory::factory()

[sebdesign]

The factory method can be called in a number of ways:

// Without arguments
User::factory();

// With count
User::factory(3);

// With count and array state
User::factory(3, ['account_status' => 'suspended']);

// With count and closure state
User::factory(3, function (array $attributes) {
    return ['account_status' => 'suspended'];
});

// With array state
User::factory(['account_status' => 'suspended']);

// With closure state
User::factory(function (array $attributes) {
    return ['account_status' => 'suspended'];
});

This PR adds docblocks for the possible arguments and cleans up the parameter overloading.