Aggregations by capture group are case-sensitive even when queries are not

Created by: felixfbecker

When the query is case-insensitive, the aggregation by capture group is not:

This leads to the unexpected case that when drilling down into a bar, it matches more results than the count of the bar, because it will also match other cases.

The expected behavior would be (I think) that the aggregation is also case-insensitive, i.e. collects all matches into a single bar test.

/cc @joelkw @felixfbecker @vovakulikov @unclejustin