IdentifiableItemCodec is only used by KeyedListNodeCodecContext
and it is used directly. Detach it from IllegalArgumentCodec, making
peeling off one possibility from the class tree.
JIRA: MDSAL-704
Change-Id: I25a818eabe80d5bb3f6b4ff2d152e7ca002a93a1 Signed-off-by: Robert Varga <robert.varga@pantheon.tech>