graphql: Add 'as' option to argument method signature (#981)

* graphql: Add test for argument method with 'as' option

* graphql: Add 'as' option to argument method signature

Author: aruma256

gems/graphql/1.12/_test/test.rb

@@ -54,6 +54,7 @@ def ping = context[:ping]
 
     field :article, String, null: false do
       argument :id, ID, required: true
+      argument :external_id, ID, required: false, as: :internal_id
     end
 
     field :error_field, String, null: false

gems/graphql/1.12/graphql.rbs

@@ -15,6 +15,7 @@ module GraphQL
         ?default_value: untyped,
         ?description: String,
         ?validates: Hash[untyped, untyped],
+        ?as: Symbol,
       ) ?{ (*untyped) -> void } -> void
     end