The only reason SearchFolder.EmailIdentifier exists was to store the
date for ordering the folder, but that can be done with any old class,
meaning we can simply pass though existing ImapDb ids to clients, fixing
a lot of bugs and corner cases along the way.
Move SearchFolder and search EmailIdentifier implementation out of
ImapDb and into its own package. Decouple both from ImapDB, and improve
the implementation, fixing a few inefficiencies. Merge search
FolderProperties into the SearchFoldern implementation as an inner
class.
Merge SearchTerm into ImapDB.SearchQuery as an inner class and move the
outer class's source down a level, since it was the only file left in
the imap-db/search dir.
Require EmailIdentifier implementations to use an outer GVariant of the
form `(yr)` (that is, a byte and an arbitrary length tuple), so that
inner representations are independent of the outer format.
The GVariant type "*" only matches a single data type, not many, and
the sense of the test to check serialised ids was wrong anyway. As a
reuslt, this method probably never worked. Add a unit test.
