When using ClippingPolygon, excluded tiles should not load

[corybarr]

Feature

In Cesium for Unreal, Unity, and Omniverse if a tile is fully excluded by the Cesium-Native equilvalent of ClippingPolygon, the tile will not load. Adding this feature in CesiumJS would enhance performance.

Sandcastle demonstrating issue.

tilesLoadWhileClipped.mp4