[prototype runtime] Fix error when output Object constants

[ksss]

Parsing for Object raises a RuntimeError.

$ bundle exec rbs prototype runtime Object
bundler: failed to load command: rbs (/Users/yuki.kurihara/.rbenv/versions/3.2.2/lib/ruby/gems/3.2.0/bin/rbs)
/Users/yuki.kurihara/src/github.com/ksss/rbs/lib/rbs/prototype/runtime.rb:574:in `const_name!': unhandled exception
	from /Users/yuki.kurihara/src/github.com/ksss/rbs/lib/rbs/prototype/runtime.rb:396:in `block in generate_constants'
	from /Users/yuki.kurihara/src/github.com/ksss/rbs/lib/rbs/prototype/runtime.rb:369:in `each'
	from /Users/yuki.kurihara/src/github.com/ksss/rbs/lib/rbs/prototype/runtime.rb:369:in `generate_constants'
	from /Users/yuki.kurihara/src/github.com/ksss/rbs/lib/rbs/prototype/runtime.rb:461:in `generate_class'
	from /Users/yuki.kurihara/src/github.com/ksss/rbs/lib/rbs/prototype/runtime.rb:54:in `block in decls'
	from /Users/yuki.kurihara/src/github.com/ksss/rbs/lib/rbs/prototype/runtime.rb:51:in `each'
	from /Users/yuki.kurihara/src/github.com/ksss/rbs/lib/rbs/prototype/runtime.rb:51:in `decls'
	from /Users/yuki.kurihara/src/github.com/ksss/rbs/lib/rbs/cli.rb:696:in `run_prototype'
	from /Users/yuki.kurihara/src/github.com/ksss/rbs/lib/rbs/cli.rb:137:in `run'

The cause is that ARGF is a special object and the class name is not correctly obtained.

This is a rare case, but the same problem can occur for all classes/modules with ARGF as a constant.

The correct type of ARGF in RBS is RBS::Unnamed::ARGFClass.

As a fix, I suggest that if the value of the constant is ARGF, the type should be RBS::Unnamed::ARGFClass.
I have also modified it so that the correct type, RBS::Unnamed::ENVClass, is applied for ENV as well.

[soutaro]

Thanks!