* 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
* enumerator.c: Use to_enum for Enumerable methods returning Enumerators.
  This makes Lazy#cycle no longer needed, so it was removed.
  Make Enumerator#chunk and slice_before return lazy Enumerators.
  [Bug #7715]

* internal.h: Remove ref to rb_enum_cycle_size; no longer needed

* enum.c: Make enum_cycle_size static.

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