fix(three-mmd-b): z flip

[Lilia-Chen]

Root cause

The problem is that PMX's default Z direction = default negative Z in three.js. Therefore, the model was mirrored by the X-Y plane.

Resolution

• build-geometry.ts: positions, normals, face winding order and morph targets are flipped.
• build-bones.ts: Z-coordinate flip for each bone.
• TODO: Given the fact that the animation loading is incomplete so far, need to remember to apply the same Z-flip to the animation trace coordinates.

Before vs After

Before: 👎

After: 👍

The bones are also correct: