Blend shape fixes for VRM1

[fire]

From Lyuma

1. not all vrm1 files will hit the head hiding code
2. some models may explicitly assign the face mesh to be thirdPersonOnly
3. some cases exist in which the same mesh will be returned
4. need to do the blendshape names in a separate step

[lyuma]

To summarize:

#94 was merged with support for the vrm-specific mesh/primitives/extras/targetNames property in the vrm 0 rotate_scene_180 function. we should document that this function also renames blendshape names

However, this code does not get hit in vrm 1.0, and there was a duplicate of this put into the face hiding code which is both redundant in vrm 0 but isn't guaranteed to be hit in vrm 1 for all meshes (with firstPersonMode!="auto"), so we should fix this at some point.

[fire]

We discussed cutting a release after adding a export option for head hiding code and default it to off.