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.
Arseny Kapoulkine