Add blendShapes and humanoid bone support to VRM + bugfixes

[magicien]

PR for vrm branch

• Features
  • Add blendShapes support
  • Add humanoid bone support
• Bugfixes
  • Fix GLTFSceneSource initializer error handling
  • Add TEXCOORD_2 and TEXCOORD_3 to GLTFTypes
    • Not yet implemented but it avoids crashes when a material has more than 2 texcoords
  • Fix the shader file references
  • Change VRM meta data to optional
• Improvements
  • Remove the submodule
  • SPM: add workaround for Foundation.Bundle to enable swift previews by @AndrewSB
  • Remove print() for debug