api,introspection: update 'Validity' property in the SMS interface

We don't want to support only 'relative' validity, so don't assume that the
Validity property will always be a uint32 value.

Instead, we define the Validity propery as '(uv)' tuple, where the first value
(a MMSmsValidityType) specifies the type of validity, and the second value is
a variant formatted accordingly to what the validity type specifies (e.g. a
uint32 value if the type is MM_SMS_VALIDITY_TYPE_RELATIVE).

src/tests/test-sms-part.c

@@ -536,7 +536,7 @@ common_test_create_pdu (const gchar *smsc,
         mm_sms_part_set_encoding (part, encoding);
     }
     if (validity > 0)
-        mm_sms_part_set_validity (part, validity);
+        mm_sms_part_set_validity_relative (part, validity);
     if (class > 0)
         mm_sms_part_set_class (part, class);