Atrifacts on labels on top of not-clamped translucent polygon

[Sandastle](https://sandcastle.cesium.com/index.html#c=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).

If you have a label rendered above a polygon that is not clamped to ground, it doesn't look good:


Artifacts are clearly visible when moving the camera. But if you clamp the polygon to the ground (set `entity.polygon.height = undefined` the artifacts disappear:


Reproduce the issue from the linked Sandcastle example with a translucent polygon whose height is set and a label rendered above it, then compare it with entity.polygon.height = undefined. Start by tracing the polygon and label rendering involved in that example; done means the camera no longer reveals visible artifacts over the non-clamped polygon.

Written by the indexing model from the issue text.