Consolidate common DeveloperError usage.

We had tons of string literals throughout Cesium with the text `This type should not be instantiated directly.`.  We also had helper functions set up in multiple files doing similar things.  This consolidates usages of this error message into a single static `DeveloperError.throwInstantionError` function.

Assuming our minimizer doesn't do fancy string literal extraction, this should also string the minimized file every so slightly as well.