Throw debugging errors in the 3D Tiles Sandcastle demos

[lilleyse]

For development/debugging purposes it would be helpful to see when errors occur when loading tileset.json or individual tiles while in the Sandcastle demos, as the current behavior just leaves an empty globe / empty tile space.

Checking for tileset.json errors is pretty easy, but checking for tile errors is more difficult as the readyPromise is not easily accessible from the outside. Would it be worth supporting a debugging event in Cesium3DTileset like tileFailed to look for these types of errors in the Sandcastle demos?

This will help save a lot of time when debugging invalid tiles.

[lilleyse]

Example case where this would help: #5353

[mramato]

I think a tileFailed event makes a lot of sense, do terrain and imagery already do something similar? We should make sure we have a holistic approach so that the architecture/API makes sense from the outside.

[lilleyse]

do terrain and imagery already do something similar

I think so, TileProviderError.handleError does something like this.

[lilleyse]

Fixed in #6088