qunit: Prepare testrunner for QUnit 2

qunit: Prepare testrunner for QUnit 2

* Nested modules:
  - Support for Sinon extension was fixed by Ib17bbbef45b2bd.
  - Support for Fixture extension was still broken, masked by the use
    of a local variable that made the handler not fail when setup ran twice
    in a row. Fixed using the same moduleStack.length check.
  - Add regression test.

* beforeEach/afterEach:
  - Added in 1.16, with compat for setup/teardown.
    Our wrapper adds its own setup/teardown, and preserves any original one.
    However, it didn't account for beforeEach/afterEach, so it ends up
    sending both but only one is used.
  - Fix to support both on the incoming localEnv object, and also switch
    our wrapper to use beforeEach/afterEach in prep for QUnit 2.0.
  - Fix our wrappers to preserve return value since QUnit 2 allows beforeEach
    and afterEach hooks to be asynchronous by returning a Promise, similar
    to how one can do from QUnit.test().
  - Add regression test.

* Centralise makeSafeEnv logic
  - We always create our own env object to pass to orgModule().
    Document why this is (to avoid recursion).
  - Add regression test.

* Custom assertion methods:
  - Use this.pushResult instead of the deprecated QUnit.push() method.
    This also improves the in-browser reporting of errors by properly
    supporting 'negative' results for notHtmlEqual reporter.

Bug: T170515
Change-Id: If4141df10eae55cbe8a5ca7a26707be1cd7b9217