On our first pass of making index use collation-aware, we disallowed using indices for queries with non-null collators that match nested objects or arrays containing strings. In order to allow index use in this case, we must:
--Update index selection. Currently if a query matches nested objects or arrays, then in order to select an index, the query and the index must both have null collators. We must remove the code that rejects indices in this case.
--Update index key generation. Currently only strings at the top level are transformed into ComparisonKeys. We must also transform strings in nested objects and arrays.
--Update index bounds building. Similarly to index key generation, we must transform strings in nested objects and arrays in our index bounds.