Remove checked-in native dependencies, use packages

[lemming104]

Most of the work here actually takes place outside of this repository. The following repositories now have GitHub actions capable of building packages (see list below). Note that these are not automatically run and must be manually triggered, then their .nupkg outputs should be audited and uploaded manually; I chose to do this rather than auto-upload them because these are slow-changing packages and I want to be VERY deliberate about when we push updates.

1. https://github.com/Helion-Engine/ZMusicWrapper: now builds both the managed wrapper for ZMusic, as well as binaries for Linux and Windows
2. https://github.com/Helion-Engine/SDLInputWrapper: now builds the SDL controller wrapper (button mapping, gyro input) as well as SDL2 for Linux and Windows
3. https://github.com/Helion-Engine/BinaryDependencies: Builds native libraries for GLFW and OpenAL-Soft; these are actually also provided by OpenTK, but they don't provide the necessary .lib or .a files for native linking in AOT builds.

[lemming104]

I have opened this PR as a draft because there are a handful of outstanding issues I intend to resolve:

1. libopenal.so needs to be renamed to libopenal.so.1 for Linux non-AOT builds, because OpenTK apparently doesn't do the fuzzy match there.
2. There are apparently some libraries floating around in the Windows build that are not built with /MT. These do not presently break the build, but I want to investigate further so it doesn't come back to haunt us later.
3. The actual Nuget packages need to be uploaded to nuget.org once (1) and (2) have been finished. I have tested locally on both Linux and Windows using a workaround that involves editing nuget.config to point to a local directory containing the .nupkg files.

[lemming104]

Looks like the library in (2) is probably SDL2.