Normal raycaster makes LOD generation process >2x slower and often
generates normals that look significantly worse compared to what the
simplifier comes up with by default. This was likely different before
last meshoptimizer upgrade, as the attribute metric was not functioning
properly, but now it looks like it's doing more harm than good.
This change makes it disabled by default but keeps an easy option to
re-enable it per mesh using LOD parameters for now until we get more
confidence and can remove the code outright.
Because the long term plan would be to disable this feature entirely,
the scripting API isn't changed, and it's just off-by-default there with
no way to re-enable.
Fixes navigation source geometry data corruption caused by thread-use that changed vertices or indices while the source geometry data was used in a parsing process or read from by the navmesh baking.
