Port test262.py to new test suite

https://codereview.qt-project.org/#/c/222439/:

The right thing to do would be to switch to the master branch of upstream, port our test262.py over to use the new test suite (but still use expectations) and use the tags that are inside the tests to selectively run all es5 tests (ensure they pass) and pick those es6 tests that we have implementations for.

Related info:

• https://github.com/tc39/test262/blob/master/INTERPRETING.md
• https://github.com/test262-utils/test262-harness-py