[Feature Request] constraint unweighted bones for the skeleton reference pose

[AchimTuran]

As a user , I want to constraint unweighted bones for the reference pose in the skeleton asset , so that I can cleanly setup my characters without leaving the Unreal Engine editor.

[AchimTuran]

CSkeletonReferencePose skeletonReferencePose(skeletalMesh->GetRefSkeleton());
          const FTransform worldTransform = skeletonReferencePose.GetRefBonePose(newBone.ConstraintBone, CSkeletonReferencePose::EBonePoseSpaces::World);
          skeletonReferencePose.SetBonePose(newBone.NewBoneName, worldTransform, CSkeletonReferencePose::EBonePoseSpaces::World);
          FTransform newBoneTransform = skeletonReferencePose.GetRefBonePose(newBone.NewBoneName);

          FReferenceSkeletonModifier referenceSkeletonModifier(skeletalMesh->GetRefSkeleton(), Skeleton);
          referenceSkeletonModifier.UpdateRefPoseTransform(skeletalMesh->GetRefSkeleton().FindBoneIndex(newBone.NewBoneName), newBoneTransform);