* enumerator.c: Fix and improve rdoc for to_enum

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@39056 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
* enumerator.c: Finalize and document Lazy.new. [Bug #7248]
  Add Lazy#to_enum and simplify Lazy#size.

* test/ruby/test_lazy_enumerator.rb: tests for above

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@39057 b2dd03c8-39d4-4d8f-98ff-823fe69b080e