To avoid the loop, how about `schema.indexedPaths()` returning a hash? with keys as paths and values as arrays of index types? So a lookup/check is essentially `indexes[this.path].indexOf('2dsphere')`?

I had coded something along those lines earlier, but then realized the value needs to be an array of index-types the path is a part of, and might end up containing sort orders that make no sense. Such as, `[ 1, '2dsphere' ]` in case the 2d-indexed field is also part of a compound index.