filterPosOp support

We need to support filterPosOp (.$[<identifier>].) in a convenient manner.

Example with KMongo:

data class Parent(val _id: String, val list: List<Element>)
data class Element(val id: String, val value: String)

override fun updateListElements(objectId: String, elements: List<Element>) {
    val setBsons = mutableListOf<Bson>()
    val arrayFilters = mutableListOf<Bson>()
    elements.filter { !it.id.isNullOrBlank() }
        .forEachIndexed { index, element ->
            setBsons.add(
                Updates.set("${Parent::list.path()}.\$[elem${index}id]", element)
            )

            arrayFilters.add(
                "{'elem${index}id': '${element.id}'}".bson
            )
        }

    col.updateOne(Parent::_id eq ObjectId(objectId), combine(setBsons), UpdateOptions().arrayFilters(arrayFilters))
}