Fix: .anims Export and Import

[effs]

Summary

Basic support for all motion animation export/import. There's very likely a lot of work left to support all cases.

• Fixed data decoding/encoding of .anims buffers
• Added decoding/encoding for track information from the buffer
• Added track and other non-buffer animation data to GLTF encoded into the extra field (there isn't really any way to represent it in the standard animations format.)

Testing

Only manually validated on a limited set of .anims

BREAKING

Previously exported .anims contain incorrect/incomplete data. Need to see about a migration path, unless it's ~trivial to fix it on the Blender side and/or using new buffer logic

Known Issues

• All .anims data isn't exported yet
• Root Motion not reimported
• Only existing animations can be edited

Additional work tracked in #1425

Dependencies

Probably needs work in the Blender plugin just to work, and definitely to use new capabilities.

Fixed

Closes #1403