Add signatures for the `main` object

Hello. The using method at the top level seems not typed. Is there a way to resolve it?

Reprodoction

The following is a reproduction using Steep. First, prepare a few files.

a.rb:

using Module.new

Steepfile:

target :test do
  check "a.rb"
end

Gemfile:

source "https://rubygems.org"
gem "steep", "1.2"
gem "rbs", "2.7"

Then, install the gems and run steep on your terminal:

$ bundle config set --local path vendor/bundle
$ bundle install
$ bundle exec steep check

You should see the following output:

a.rb:1:0: [error] Type `::Object` does not have method `using`
│ Diagnostic ID: Ruby::NoMethod
│
└ using Module.new
  ~~~~~

Detected 1 problem from 1 file

Environment

• ruby 3.1.2p20 (2022-04-12 revision 4491bb740a) [arm64-darwin21]
• rbs 2.6.0 2.7.0
• steep 1.1.0 1.2.0

Note

The Module#using method signature has been existing already:

https://github.com/ruby/rbs/blob/95667d76c725566fa455bbcca0c10cc1e539475a/core/module.rbs#L1519

Reproduce the report with a.rb, Steepfile, and Gemfile using the documented Steep command. Compare the existing Module#using signature in core/module.rbs with the signatures available to the top-level main object; done means steep check accepts using Module.new without the reported Ruby::NoMethod error.