Function blender_armature::flatten_exported_armatures

pub fn flatten_exported_armatures(
    armatures_by_filename: &ArmaturesByFilename
) -> Result<HashMap<&str, &BlenderArmature>, FlattenArmatureError>

Convert ArmatureeshByFilename into a HashMap<ArmatureName, BlenderArmature> that flattens all of the armatures across all of the files into one HashMap.

This will error if there are two armatures with the same name across two or more files.