tests: Add ringer tests

We mock libfeedback and CallsCall to test the ringer for the following
scenarios:
- Call state changes
- User requested silencing of ringer
- Multiple calls

tests/mock-libfeedback.h

@@ -0,0 +1,28 @@
+#pragma once
+
+#define LIBFEEDBACK_USE_UNSTABLE_API
+
+#include <libfeedback.h>
+#include <glib.h>
+
+
+gboolean        __wrap_lfb_init                            (const char *app_id,
+                                                            GError    **error);
+void            __wrap_lfb_uninit                          (void);
+void            __wrap_lfb_event_set_feedback_profile      (LfbEvent   *self,
+                                                            const char *profile);
+
+void            __wrap_lfb_event_trigger_feedback_async    (LfbEvent           *self,
+                                                            GCancellable       *cancellable,
+                                                            GAsyncReadyCallback callback,
+                                                            gpointer            user_data);
+gboolean        __wrap_lfb_event_trigger_feedback_finish   (LfbEvent     *self,
+                                                            GAsyncResult *res,
+                                                            GError      **error);
+void            __wrap_lfb_event_end_feedback_async        (LfbEvent           *self,
+                                                            GCancellable       *cancellable,
+                                                            GAsyncReadyCallback callback,
+                                                            gpointer            user_data);
+gboolean        __wrap_lfb_event_end_feedback_finish       (LfbEvent     *self,
+                                                            GAsyncResult *res,
+                                                            GError      **error);