Note: this change completely overwrites the meshoptimizer library source
(from git SHA c21d3be6ddf627f8ca852ba4b6db9903b0557858)
without including any patches; a distance error metric patch is still
needed and will be reapplied in the next commit.
The changes elsewhere are due to a signature change for
meshopt_simplifyWithAttributes.
-Reworked how meshes are treated by importer by using EditorSceneImporterMesh and EditorSceneImporterMeshNode. Instead of Mesh and MeshInstance, this allows more efficient processing of meshes before they are actually registered in the RenderingServer.
-Integrated MeshOptimizer
-Reworked internals of SurfaceTool to use arrays, making it more performant and easy to run optimizatons on.
