Need reference implementations for cesium-native users

[Brian Langevin]

It could be useful to have a set of "how to get started examples" for anyone wanting to integrate cesium-native into their project for the first time.

This would be a little different from just referencing Cesium for Unreal or Cesium for Unity in that these examples would be as simple as possible to help guide the user through integration.

There could be multiple reference examples:

• A C++ application integrating all of cesium-native to stream tiles
• A C++ application integrating only parts of cesium-native (Ex. load Gltfs only)
• A non-C++ application integrating cesium-native (C#, web assembly, etc)

Ideally, these examples would also be built by CI, to make sure any supported use cases are always working.

Feel free to chime in with other ideas as well.