The Godot-specific patch is just a single line now; removing this patch
will likely require adjusting Godot importer code to handle error limits
better.
This also adds new SIMPLIFY_ options; Godot is currently not using any
of these but might use SIMPLIFY_PRUNE and SIMPLIFY_SPARSE in the future.
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.
