Better error handling for 3D Tiles styling

3D Tiles styling will fail silently if there is (any?) syntax error.

Try going to the Point Clouds styling example:

https://cesiumjs.org/Cesium/Build/Apps/Sandcastle/?src=3D%20Tiles%20Point%20Cloud%20Classification.html

(you might need to try it locally if the hosted version isn't working, see https://github.com/AnalyticalGraphicsInc/cesium/issues/7731).

Then change any of the `===` to `==`, the styles will not be applied and there will be no warning or error. This threw me off because I didn't realize the `==` was actually not a valid operator in the styling language. As far as I was aware, the problem was that the point cloud I was working with just didn't have this id or property name.

Open the 3D Tiles Point Cloud Classification Sandcastle example and reproduce the issue by changing a styling operator from `===` to `==`; try locally if needed using the linked issue for context. Trace the styling failure path and determine where syntax errors are discarded. Done means invalid styling produces a useful warning or error instead of failing silently.

Written by the indexing model from the issue text.