Add a basic high-level wrapper over some of the Assimp APIs

In our [current 2.0 Assimp bindings](https://github.com/Ultz/Silk.NET/tree/2.0/src/Assimp) we only expose 1:1 native bindings which are generated by our BuildTools generator. This is good, however it isn't very user friendly as it involves a lot of usage of unsafe and other native paradigms that aren't easy for beginners (you can see an example of it being used [here](https://github.com/john-h-k/Voltium/blob/7196b7d3e91dc79aaa29e84410c049e283345f60/sources/Voltium.ModelLoader/ModelLoader.cs) and it's not as pretty as it could be)

Similar to [assimp.net](htps://github.com/assimp/assimp-net), we'd like to expose a higher-level managed wrapper on top of our low-level bindings so that it's easier to use and easy for people who've never used Assimp before to pick up. This could be done in steps, for example in one PR laying out an API surface, and slowly implementing it in subsequent PRs.

If you have any further questions feel free to join [our Discord server](https://discord.gg/DTHHXRt) - we're pretty much always active there.