Currently, a lot of our build variables that are defined at
configuration time, are spread out across the code base, often declared
as `extern` which can break when moving around sections of the code
across files.
This commit introduces a "Config" namespace which basically maps to the
definitions in `config.h`, but allows us to properly access them too
from the Vala source code.
By doing so, it helps us to more explicitly see where we rely on a
build variable from this file (which should be obvious from the `Config'
namespace).
To make it ourselves a bit easier in Meson too, we can declare an
internal dependency, which helps ensure that we pull in the dependency
where needed.
Engine mocks don't need to be in the `Geary` namespace, and including
them there makes it difficult to use them in client tests, so put them
all in their own name-space and corresponding directory.
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.
