Some servers (e.g. Dovecot) use placeholder strings instead of the empty
string (e.g. "MISSING_DOMAIN") in FETCH Envelope responses when a
required address part (e.g. local part, domain) are empty.
This adds a quirk that can be enabled for such servers to check for the
placeholders and if found, replace them with empty strings.
Add a quirks object as a property so code that parses the response has
access to it. Simplify constructing server responses slightly and pass
the IMAP connection's quirks when doing so.
* test/api/*.vala: Renamed files that contained mock objects to *-mock.vala,
not *-test.vala.
* test/testcase.vala: Renamed to test-case.vala for consistency, remove
TestCase class from Gee package since that's really not true. Clean up
code for consistency.
* test/meson.build, test/CMakeLists.txt: Split TestCase compilation out
into a separate test lib.
