WL#1879: Decreasing size of operation records

Affects: Benchmarks-3.0   —   Status: Un-Assigned

Currently the operation records are fairly "spacy".
An optimisation is to decrease the size of them
significantly. In DBTC as an example it should be possible to decrease
to 8 bytes per operation after the prepare phase.

Also TC take-over could use separate records which are smaller in size
and specialised for TC take-over.

5.0 or 5.1 feature