Layers do not support (or poorly documented) creating SDE or Parse/UnparseErrors

From what I can tell, there is no way for a layer signal that an error occurred, or at least non of our current layers seem to check and handle any errors, so if it can be done it needs better examples.

If a we do something like layerRuntimeInfo.runtimeData.SDE(...), then that SDE exception is caught by the layer infrastructure and turned into a LayerExecutionException, which seems like it's used to indicate bugs in a layer. Throwing an SDE should not be considered a bug.

It looks like some functions do provide ParseOrUnparseState, so maybe we could create a Parse/UnparseError, but it's not exactly clear or documented if/how this should be used, or even if the layer infrastructure checks the state. This needs some clarification.