The `test/language/generators/` directory contained a single file that
concerned generators derived both from syntactic form and from a
built-in function.
Refactor this test into two files and place each in the appropriate
directory.
These tests are derived from the following files within the Google V8
project:
test/mjsunit/es6/generators-iteration.js
test/mjsunit/es6/generators-objects.js
test/mjsunit/es6/generators-runtime.js
test/mjsunit/es6/generators-states.js