- Expand ambiguous assertion messages and assert execution paths more
finely.
- Improve variable names in `for..of` tests
While the object created by a GeneratorFunction may be considered an
"iterable", it is being used as an iterator in these tests. Naming the
variable according to the way it is used improves the readability of
the test body.
- Add 'features' attribute to test frontmatter
- Move tests
- Introduce additional `for..of` control flow tests
