call: Add call-type property

The designs for the call details show information on the type of the call:
https://gitlab.gnome.org/Teams/Design/app-mockups/blob/master/calls/calls.png
So f.e. "Cellular", "Matrix WebRTC Video Call".

These properties can potentially also be useful in choosing the mechanism to
use for the audio controls from the call display.

src/calls-ui-call-data.c

@@ -652,6 +652,21 @@ calls_ui_call_data_get_ui_active (CallsUiCallData *self)
   return self->ui_active;
 }
 
+/**
+ * calls_ui_call_data_get_call_type:
+ * @self: a #CallsUiCallData
+ *
+ * Returns: The type of call, or #CALLS_CALL_TYPE_UNKNOWN if not known.
+ */
+CallsCallType
+calls_ui_call_data_get_call_type (CallsUiCallData *self)
+{
+  g_return_val_if_fail (CALLS_IS_UI_CALL_DATA (self), CALLS_CALL_TYPE_UNKNOWN);
+  g_return_val_if_fail (CALLS_CALL (self->call), CALLS_CALL_TYPE_UNKNOWN);
+
+  return calls_call_get_call_type (self->call);
+}
+
 /**
  * calls_call_state_to_cui_call_state:
  * @state: A #CallsCallState