[CX] Report query evaluation statistics

The current query plan does not provide a lot of information to reason about the query performance.
It shows (a subset of) the operators that are use to evaluate a query, but there is no information about

• the cardinalities of intermediate results,
• the size of intermediate results, or
• the evaluation times for operators or subplans.

To allow a query writer to reason about and improve the performance of a query such information should be provided.

Once this information is available it should also be possible to see this information as annotation on the query plan.