Fix errors in morph normal encoding in quantize() and meshopt()

[donmccurdy]

Fix errors in quantization and meshopt compression of morph normals and tangents.

• Morph normals and tangent deltas are not normalized vectors, and should be quantized, not filtered

• Clamp morph normals and tangents to [-1, 1]

• Extend quantize() options to disambiguate vertex attributes from morph attributes

• Fixes #1142