Enable importing & exporting VCards

This commit adds the experimental functionality in Contacts to import
VCard (*.vcf) files.

Since importing a contact means we have to take in untrusted/unvalidated
input, let's give a high-level view of what happens:

* Contacts starts a native file chooser dialog so the user can choose
  which file to import
* According to the chosen file, Contacts will launch a subprocess to do
  the actual parsing using a `Contacts.Io.Parser`. At this point, we
  only have a single subclass, which allows importing VCards.
* The helper process serializes the result to a `GLib.Variant`, and
  sends it to the main process, which will receive the result and
  parses it again.
* After the parsing operation is done, we can then start up a
  `ImportOperation`, which will import the contacts using libfolks' API.

Exporting contacts is quite a bit easier, since we don't have to deal
with untrusted input: we serialize the list of selected contacts and
asynchronously write each to the given output stream. In the app, that's
a user chosen file; in tests, that can be a string.

Fixes: https://gitlab.gnome.org/GNOME/gnome-contacts/-/issues/1
Fixes: https://gitlab.gnome.org/GNOME/gnome-contacts/-/issues/38

1 files changed, 1 insertions, 0 deletions

diff --git a/vapi/config.vapi b/vapi/config.vapi
index 45fb07e..090d8c5 100644
--- a/vapi/config.vapi
+++ b/vapi/config.vapi
@@ -16,5 +16,6 @@ public const string GETTEXT_PACKAGE;
 /* Configured paths - these variables are not present in config.h, they are
 * passed to underlying C code as cmd line macros. */
 public const string LOCALEDIR; /* /usr/local/share/locale */
+public const string LIBEXECDIR;
 }