Also remove the onlyStrict restriction as the class body is always on strict mode and
the failures are still valid

Closes #1634.

This should be well covered in the syntax templates and opens the path for tests with module code restrictions

- Add cases for mixing module and script code
- Rename test case from return promise to thenable
- Fix script code case with valid loaded fixture
- Add a test to assert a promise return
- Add case for specifier toString rejection
- Add case for specifier toString
- Test Assignment expression abrupt completion
- Test Promise return