UAnimSingleNodeInstance doesn't sample notifies on montage animation tracks

Notifies that are placed on animations referenced by montages aren't triggered when using the UAnimSingleNodeInstance to play back the montage. This is because - unlike on UAnimComposite - there is no implementation of GetAnimNotifiesFromDeltaPositions for UAnimMontage. And UAnimSingleNodeInstance::SetPositionWithPreviousTime relies solely on GetAnimNotifiesFromDeltaPositions to sample notifies on the assets that are being played back. We don't hit this issue with regular playback of montages because FAnimMontageInstance::HandleEvents manually samples both the montage track, and the animation tracks of the montage (similar to UAnimComposite::GetAnimNotifiesFromDeltaPositions).
We should do one of the following:

• Change UAnimSingleNodeInstance::SetPositionWithPreviousTime to sample both the montage notify track and the animation notify tracks
• Implement UAnimMontage::GetAnimNotifiesFromDeltaPositions. This would mean changing FAnimMontageInstance::HandleEvents to account for the change.
• Change UAnimSingleNodeInstance::SetPositionWithPreviousTime to call FAnimMontageInstance::Advance rather than UAnimSequenceBase::SetPosition when dealing with montage assets. This would go down the regular montage codepath and handle the notifies via FAnimMontageInstance::HandleEvents

1. Open an animation in the animation editor
2. Add a sound effect notify on any frame
3. Create a new montage
4. Add the previous animation as a track on the montage
5. Place another sound effect notify on one of the montage notify tracks
6. Play the montage within the montage editor
   1. Note how two sound effects are triggered (one for the notify on the montage, one for the notify on the animation)
7. Now use the buttons to step frame by frame through the montage
   1. Note how when you get to the frame where the notify is placed on the montage, it's triggered. But on the frame where the animation's notify should be triggered, nothing happens