Support faker for custom scalars

[ardeois]

scalars option allows to use custom generator function from casual

Now we have generateLibrary supporting faker, we should allow custom generator functions from faker as well

[MH4GF]

memo:

• casual is only one level with property calls, like this: country => casual["country"] // 'United Kingdom'
  • Some generators may be function calls that specify arguments: integer => integer(from = -1000, to = 1000) // 632
• faker is a nested and method chain: faker.address.country() // 'Greece'

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This is an interface similar to casual 🤔 : address.country => faker["address"]["country"]()

[stale[bot]]

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