Improve the architecture to support multiple dictionaries.

This change enables the interface to get multiple dictionaries from a
dictionary pack. It only implements it to the end in the case of the
proprietary method, as the open method needs still some working out,
and the "inside the package" method does not need it.

This change goes together with Iaa95bf36, and breaks the build
without it.

Bug: 1752028

Change-Id: I3ccfd696e8ef083ef9c074e1c3e4bb0bf2fcfd23