In SERVER-103827, we are adding very basic support for estimating residual filters with index CE. We will support only residual filters that are over a single predicate that can be translated into exact bounds over a single index. For example, given a residual filter with sargable predicates on "a", we could estimate it if there was an index on "a". Note that we support estimating an AND expression where all children are on the same field.

This ticket is to support more complex residual filers. For example, given a residual filter with sargable predicates on "a", "b", and "c", we could estimate it if there was an index on "a" and a separate index on "b" and "c".

This may involve some interesting decisions. For example, given a residual filter with sargable predicates on  "a", "b", and "c" and indexes {b: 1, a: 1} and {b: 1, c: 1}, we need to be careful when deciding if & how to support this.

Note: this ticket will likely be moved out of the spike