Implement dynamic 3D Tiles SSE adjustment from CesiumJS

[kring]

CesiumJS dynamically adjusts the screen-space error according to several heuristics. We should implement those here.

[kring]

For 3D Tiles, CesiumJS uses a higher max SSE value when the camera is moving quickly. While thinking about implementing this in cesium-native, it occurred to me that adjusting SSE might not be the right way to go. Instead, we should try:

• reducing loadingDescendantLimit from 20 down to maybe 4 or 5 or something. This will cause lower-detail tiles to be preferenced during the flight, but higher-detail tiles will still be loaded eventually if the computer/connection is fast enough.
• reducing the maximumSimultaneousTileLoads from 20, again maybe to 4 or 5. So the load queue doesn't get so full of tiles we soon won't need.
• setting preloadAncestors and preloadSibilings to false, so these not-strictly-necessary tiles won't be loaded at all.

I think this will work better than changing the max SSE, which (unless we take pains) will cause detail to disappear as the camera accelerates.