Polyline rendering is choppy/glitchy at extreme camera angles and when clamped to ground

Sandcastle example: [Sandcastle Example](https://sandcastle.cesium.com/#c=nVLLTsMwEPwVK5cGKXV4FCFBWoEKgkMREa8L4eA2S2vheKO1kypF/XecR0UoN/aUHc/Mjr0pBbFSwhqIjZmGNZuCkUXGXxvMHyyadoraCqmBBgcXiU506VR5QbmCKyJcO2nrwUFbaSUYLtLU/0o0c6VFBuycDeJGwIwlIZcry0QjFZatoO4HQUvPUVXKzXKSzqBFjTNGbRzcRZwKsu5L6BP+QZhdw5IAjAskqrvG0fhvw7PTgI1OAnZ6WFfwY/jPGh4d/3J8P+h5rmVqVy7gqD8oExZICuXw3vvG3S2b97vvKDFhDmQrf3dDVEg8fnmMZzf9OQslsvwZbwkLnZ4zSwW0h9tEb7sNtfvYIGbP6O9tp6Z4gRcZWymYtNJLmeVIlhWkfM5DC1muXCwTzovFJ1i+MI0sCneiKJUlk+k48fb+kcSrAxrjTj4KpZ7kBhJvEoWO/0umUKRSLx9KICWqmrI6msxakHMeha79q7KIai6o5/gN
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Browser: Chrome

Operating System: Windows 10

Description: It appears when clamping to ground a Polyline entity that has the arrow material, that the end of the arrow is glitching/choppy. It's more noticeable with larger width arrows. Check out the sandcastle above.


Start by opening the linked Sandcastle example in Chrome on Windows 10 and reproduce the choppy Polyline arrow when it is clamped to ground at extreme camera angles and larger widths. Trace the Polyline rendering and ground-clamping path from that reproduction; done means the arrow end renders smoothly in the reported cases without regressions.

Written by the indexing model from the issue text.