Billboard close to the terrain

[mylove10086]

When cesium has terrain and the number of billboard entities is greater than 10,000, when using Cesium.HeightReference.RELATIVE_TO_GROUND to set the grounding position of the billboard, it takes a long time for the billboard to move to the ground and cesium keeps refreshing the position of the billboard. Is there a better suggestion for this

[OmarShehata]

I believe the underlying issue here is that globe.pick(), which is used to find the terrain height at any point for each entity, needs to be optimized. There's an issue open for this here: #8481