Inline sorbet mode

[dduugg]

Is your feature request related to a problem? Please describe.
I would like an option to place Sorbet sigs in the source file, rather than a separate .rbi file, to make use of the sorbet-runtime.

Describe the solution you'd like
To use the example in the README, given:

module Example
  class Person
    # @param name [String] The name of the Person to create.
    # @param age [Integer] The age of the Person to create.
    # @return [Example::Person]
    def initialize(name, age)
      @name = name
      @age = age
    end

    # @return [String]
    attr_accessor :name

    # @return [Integer]
    attr_accessor :age

    # @param possible_names [Array<String>] An array of potential names to choose from.
    # @param possible_ages [Array<Integer>] An array of potential ages to choose from.
    # @return [Example::Person]
    def self.construct_randomly(possible_names, possible_ages)
      Person.new(possible_names.sample, possible_ages.sample)
    end
  end
end

I would like to be able to transform the file into:

module Example
  class Person
    # @param name The name of the Person to create.
    # @param age The age of the Person to create.
    sig { params(name: String, age: Integer).void }
    def initialize(name, age)
      @name = name
      @age = age
    end

    sig { returns(String) }
    attr_accessor :name

    sig { returns(Integer) }
    attr_accessor :age

    # @param possible_names An array of potential names to choose from.
    # @param possible_ages An array of potential ages to choose from.
    sig { params(possible_names: T::Array[String], possible_ages: T::Array[Integer]).returns(Example::Person) }
    def self.construct_randomly(possible_names, possible_ages)
      Person.new(possible_names.sample, possible_ages.sample)
    end
  end
end

Note that I've kept the docstrings, and only scrubbed the types from the YARD annotations, bc the yard-sorbet plugin can merge the two when generating YARD docs.