headingPitchRollToQuaternion should be calculated counter clock wise

[ggetz]

As per this discussion on the forum: https://groups.google.com/forum/#!topic/cesium-dev/2-Fn_8yeurY

[kaktus40]

Hello, I make a pull request but I think that this PR should be completed with an articles that explains how to change.

[ggetz]

@kaktus40 We'll update the forum page as soon as the PR is in and the issue is closed! Thanks!

[pjcozzi]

Related forum post: https://groups.google.com/forum/?hl=en#!topic/cesium-dev/bsPTytXzNqc

[hpinkos]

This was initially added in #5848 but we decided to revert it before the release because it was too big of a breaking change. See the discussion in #5868.
Changes are currently parked in the ccw-hpr branch

How do we want to move forward with this? Is this a change we ultimately want to make or should this be a "won't fix"?

If clockwise is what the FAA suggests, maybe that's the standard we should stick with. It doesn't seem like this is standardized across the board, so the only benefit I see for making the switch to CCW would be to be consistent with Cesium's other rotations (like setting a rotation for a rectangle) or to be consistent with other AGI software (but I'm not sure how much of a priority that is).