Avatars have same limitation between iOS and Android, so they would have same data in most cases. But currently we need to upload twice.
Avatars have hard limitation unlike worlds (especially, shaders are very limited), so it would be easier and more accurate than world conversion.
Cases:
  1. The avatar has iOS build -> Use it.
  2. The avatar has Android build, but no iOS build -> Convert it at runtime.
  3. The avatar has no mobile builds -> Use imposter or fallback.