Closes #2256

When checking deep equality on Map instances (including maps nested in
other collection types) we allow keys which are instances of other
collection (and don't have a useful `operator ==`) and keys which are
`Condition` callbacks that could potentially match multiple keys of the
actual value. This is maximally flexible, but it loses the nested path
information we are otherwise able to keep for iterables compared by
index.

Check whether expectation maps have any keys which need this special
treatment, and if not, special case to an algorithm close to the
`Iterable` algorithm which can enqueue nested checks and maintain the
direct known path into the collection.

Update the doc comment to describe the new behavior. This does
potentially introduce confusion since a change which adds a `Condition`
key has to potential to make _other_ keys in the same expectation
behaved differently. The benefit is a more actionable failure output for
the much more common case of checking expectations with hardcoded keys.