Add a cop to enforce prepare argument as a Symbol or String

[DougEdey]

I've been working a lot with Sorbet and introduced better support for GraphQL Prepare Methods including adding support for the prepare method to be defined on the current class

Using the upstream example for graphql-ruby

class AddInstrument < GraphQL::Schema::Mutation
    class << self
      def prepare_name(value, context)
        value.capitalize
      end
    end

    null true
    description "Register a new musical instrument in the database"

    argument :name, String, prepare: :prepare_name
    argument :family, Family

    field :instrument, InstrumentType, null: false
    # This is meaningless, but it's to test the conflict with `Hash#entries`
    field :entries, [InstrumentType], null: false
    # Test `extras` injection
    field :ee, String, null: false
    extras [:execution_errors]
    def resolve(name:, family:, execution_errors:)
      instrument = Jazz::Models::Instrument.new(name, family)
      Jazz::Models.data["Instrument"] << instrument
      {instrument: instrument, entries: Jazz::Models.data["Instrument"], ee: execution_errors.class.name}
    end
  end

This cop isn't enabled by default because I don't think everyone wants this, but we've found that removing lambdas makes our codebase much more effective to test, and easier to read, and the combination of sorbet/tapioca makes it even more effective to write & maintain code.

This cop by default will raise offenses when a block argument is provided, and request that a string or symbol is provided. but can be configured to require a string XOR symbol based on EnforcedStyle

[DougEdey]

I'm not sure why Rubocop 0.90.0 is failing

[DmitryTsepelev]

Hey hey, LGTM, thank you! Maybe rubocop works wrong because I updated the version in the master recently. I'm going to merge as is and fix right in the master