Chunk STL Export to avoid allocation errors

[philippotto]

Exporting large meshes to STL can result in "RangeError: Array buffer allocation failed". One theory is that the allocation only fails because one large consecutive array is allocated. Allocating multiple smaller arrays could work (tested by allocating two 1-GB arrays vs one 2-GB array). Since the STL is wrapped into a Blob anyway, one could build multiple STL chunks and put them into a blob, too.

Note that this would need to change the STLExporter implementation which was copied from the three-js repository.

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