[OpenAPI]: Parse basic Blueprinter fields: identifier, field, and fields

[Abishekcs]

closes #289

What this PR does?

Adds support for parsing basic Blueprinter fields:

• identifier
• field
• fields

Also supports:

• Field renaming via the name: option (e.g. field :email, name: :login)
• Block fields (e.g. field(:full_name) { |u| ... }) , defaults to string type since the block can't be statically evaluated
• Collections via Array<UserBlueprint> or [UserBlueprint] syntax

Sample Code

• routes.rb

Rage.routes.draw do
  root to: ->(env) { [200, {}, ["It works!"]] }

  get "/users/:id/blue", to: "users#show_blue"
end

• products_controller.rb

class UsersController < RageController::API
  
  # @response UserBlueprint
  def show_blue
    user = [{ uuid: 1, id: 101, name: "Alice", email: "alice@example.com", age: 25, first_name: "Alice", last_name: "loom", abishek: 'abi' }]
    render json: UserBlueprint.render(user)
  end
end

• user_blueprint.rb

class UserBlueprint < Blueprinter::Base
  identifier :uuid
  
  fields :id, :name, :email, :age
  
  field :email, name: :login   # -> "login": string

  field :abishek, name: :ad   # -> "login": string
  
  fields :first_name, :last_name

  field(:full_name) { |u| "#{u[:first_name]} #{u[:last_name]}" }
end

Screenrecording

• Before

Before.mp4

• After

After.mp4

collection

After.Collection.mp4

[Abishekcs]

Hi @rsamoilov can you review this PR whenever you're free. Thank you!

[rsamoilov]

Hey @Abishekcs ,

I'm so sorry about the delay! I'll be looking closely into the changes this weekend.

[Abishekcs]

No worries. Take your time.

[rsamoilov]

Hi @Abishekcs ,

This looks great, and I like the tests too!

Several observations:

1. the parser currently only supports symbol field names, although Blueprinter works fine with string fields too:

class UserBlueprint < Blueprinter::Base
  fields "id", "name", "email", "age"
end

2. One of the guarantees Blueprinter provides for the identifier fields is that "When rendering, identifier fields are always sorted first, before other fields". Let's also ensure identifiers are rendered first in the OpenAPI spec.