Fix KML ground overlay distortion bug

[juburr]

Fixes #5914

[cesium-concierge]

Welcome to the Cesium community @jburr-nc!

Can you please send in a Contributor License Agreement (CLA) so that we can review and merge this pull request?

I am a bot who helps you make Cesium awesome! Thanks again.

[hpinkos]

Awesome! Thanks for fixing this @jburr-nc!
Could you add a unit test? I imagine it will be similar to this one, just check that stRotation is also correct: https://github.com/AnalyticalGraphicsInc/cesium/blob/master/Specs/DataSources/KmlDataSourceSpec.js#L794-L812

As soon as we receive your CLA we'll be able to merge this.

[juburr]

@hpinkos The CLA for Novetta should be submitted. I added an additional check to the rotation test that was already there. Would you prefer a brand new test instead?

[hpinkos]

Thanks, I can confirm that we have your CLA. And that test looks fine to me!

Thanks again @jburr-nc!