Implement Postal Code Generator using Positional Generator for locale `nl`

[thdaraujo]

In lib/locales/nl.yml, there is a very large definition for a generator with over 2000 characters to be used by the regexify method.

My understanding, based on this discussion is that any combination of 2 uppercase characters are valid, except for SA, SS, and SD.

Instead of implementing a way to exclude the invalid combinations, the locale specifies all the 673 repeated permutations of possible 2-letter words that are valid. This seems very excessive to me.

AA, AB, AC, ... ZZ.

I think we could simply implement this with a generator for the postal code excluding using the positional generator instead.

[stefannibrasil]

faker japanese has more than 120k values for postcode 🤯 https://github.com/faker-ruby/faker/blob/2258715a7b2b2cf8dc680abb57eea6eeac81651a/lib/locales/ja/address.yml

[stefannibrasil]

The only way to use the positional generator would be to check for the 'nl' locale and then do something different for it:

def nl_post_code
  PositionalGenerator.new(:string) do |gen|
    gen.group(name: :digits) do |g_|
      g_.int(length: 4)
    end

    gen.lit(" ")

    gen.group(name: :letters) do |g_|
      g_.letter(length: 1, ranges: ['AA'...'SA', 'SB'...'SD', 'SE'...'SS', 'ST'..'ZZ'])
    end
  end.generate
end

However, this could become too complex if another locale has historical reasons for us not to generate a specific value. And not sure if having a custom code like the one above would be better than the explicit 2000 combinations defined in the locale 🤔