Fix BIM tileset in clipping planes sandcastle

[lilleyse]

Fixes #8053

The previous code only works if the tileset transform and bounding sphere center are along the same surface normal, which was true of the point cloud but not the BIM tileset in the 3D Tiles Clipping Planes sandcastle.

[cesium-concierge]

Thanks for the pull request @lilleyse!

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• Cesium Viewer works.
• Works in 2D/CV.
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[OmarShehata]

Thanks @lilleyse . Can confirm this fixes the issue.