Added BitSetIteratorTest.IterationOrder

Bug: angleproject:2634
Change-Id: I0e9c6ad4d19bbb7d691e46b7ec720e918b170371
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2520956
Commit-Queue: Alexey Knyazev <lexa.knyazev@gmail.com>
Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org>
Reviewed-by: Jamie Madill <jmadill@chromium.org>