Instrument IndexOrDocValuesQuery to report on its decisions

### Description

For Amazon Product Search, we use `IndexOrDocValuesQuery` and have changed it to take a listener type object that records and reports on the decision the query has made. We look at how often it picks indexed vs doc values and we can see if there are changes in the frequency with which we take each branch. Would this be a welcome addition?

Start by locating IndexOrDocValuesQuery and examining how it chooses between indexed values and doc values. Define the listener API and reporting behavior with the maintainers, then add coverage showing that each decision is reported correctly.

Written by the indexing model from the issue text.