Introduce CallsUiCallData to feed CuiDisplay

We need a proxy object because implementing the CuiCall interface in the
CallsCall base class has it's own set of problems (f.e. the "state" property
would have a type collision CallsCallState vs CuiCallState).

src/calls-ui-call-data.h

@@ -0,0 +1,17 @@
+#pragma once
+
+#include "calls-call.h"
+
+#include <cui-call.h>
+#include <glib.h>
+
+G_BEGIN_DECLS
+
+#define CALLS_TYPE_UI_CALL_DATA (calls_ui_call_data_get_type ())
+
+G_DECLARE_FINAL_TYPE (CallsUiCallData, calls_ui_call_data, CALLS, UI_CALL_DATA, GObject)
+
+CallsUiCallData         *calls_ui_call_data_new       (CallsCall       *call);
+CallsCall               *calls_ui_call_data_get_call  (CallsUiCallData *self);
+
+G_END_DECLS