journal: Invert verify entry <=> data consistency checks

journal: Invert verify entry <=> data consistency checks

Previously, for each entry in a data object's entry array, we'd check
if one of that entry's entry items referred to the data object.

Instead, when verifying the main entry array, let's check if for each
entry item found by iterating the main entry array, the corresponding
data object's entry array refers to that entry.

This enables us to re-use more code from journal-file and turns out to
be roughly 10s faster when verifying my 4G laptop journal.

When verifying data objects, we still check if every entry in the data
object's entry array also exists in the main entry array so that we ensure
we're not missing any entries when iterating the main entry array.