Draft: Add basic state tracking to the host-side positions buffer

Tracking the state of the host-side buffer will allow to make the conditionals on where the copy is executed simpler. The state can be:

1. Consistent, when the data on the host-side is consistent with the device-side counterpart.

2. InTransit, when the device to host copy was issued, but may not be completed yet.

3. Invalid, when buffer was or is being updated on the device and this is not yet reflected on the host side.

Refs. #3988

Refs. #3020