Race condition in Cesium3DTileset.memoryAdjustedScreenSpaceError

[jjhembd]

If a Cesium3DTileset is constructed with maximumCacheOverflowBytes: 0, it is possible for the screen space error adjustment to enter an infinite loop.

There are two adjustments to the screen space error that can happen depending on the current memory usage of the tileset (see #11310):

1. When Cesium3DTileset.totalMemoryUsageInBytes increases above cacheBytes + maximumCacheOverflowBytes, the memoryAdjustedScreenSpaceErrror will be increased until the requested tiles use less than cacheBytes + maximumCacheOverflowBytes
2. When memory usage drops below cacheBytes, then memoryAdjustedScreenSpaceError will be adjusted lower, until either (a) the requested tiles use more than cacheBytes, or (b) memoryAdjustedScreenSpaceError is equal to the user-defined maximumScreenSpaceError

If maximumCacheOverflowBytes is less than the size of one tile, then either adjustment can potentially trigger the other adjustment, resulting in an infinite loop.

At a minimum, we need to clarify the docs:

• The doc for maximumCacheOverflowBytes should include some guidance on good minimum values
• The read-only memoryAdjustedScreenSpaceError is important information for the user, and should be exposed and documented (it is currently set to private)