RelMdPopulationSize should use mq.getRowCount(rel) instead of rel.estimateRowCount(mq)

A few locations in Calcite call rel.estimateRowCount(mq) when they should instead call mq.getRowCount(red).

We detected this because we implemented row count estimation entirely within an alternative handle instead of RelMdRowCount, and then override estimateRowCount to ensure the custom handler is user, by throwing an unreachable code exception.

A few places in Calcite trigger these unreachable exceptions because they do not use mq.getRowCount.

The most easily triggered on is in RelMdPopulationSize for the Values parameter.