Share a single vertex list between submeshes in the exported mesh, which
makes the blend target vertex list indices line up correctly.
As a bonus, the exported FBX file will be smaller for meshes with more
than one submesh, since we're not duplicating vertices anymore.
* Replace C++/CLI components with P/Invoke
* Deleted C++/CLI projects
* Use Utf8StringHandle to marshal UTF-8 strings
* Use plaform-default calling convention
* Handle DLL preloading on Linux and macOS
* Change intermediate and output directories of native projects
* Improve P/Invoke documentation
