FilteredCollection should copy modelId method from underlying collection, but doesn't

An underlying collection might, for whatever reason, have multiple models with identical `id`s. This is fine, if the underlying collection has an overridden `modelId` method that distinguishes between those models.

FilteredCollection falls back to the default `modelId`. Hence, if two models in the underlying collection both pass the filter criterion and also have identical `id`s, then they should be both present in the filtered collection, but only one will actually be retained.

Solution: in the FilteredCollection constructor, copy the `modelId` method from the underlying collection.

Start at the FilteredCollection constructor and compare its modelId behavior with the underlying collection. Verify that a filtered collection preserves the underlying collection's modelId behavior and retains both matching models with identical ids.

Written by the indexing model from the issue text.