[FL-3833] Furi: event loop (#3675)

* Furi: epoll prototype

* Gui: simplify view_dispatcher custom event processing

* Furi: add missing critical sections to epoll

* Furi: add epoll unit tests, fully implement level processing for in and out events

* Furi: properly trigger epoll item event on adding mq, update tests.

* Unit tests: cleanup defines

* Furi: protect epoll from modification in callback

* Furi: rename epoll into event_loop, cleanup api naming

* Sync API Symbols

* Furi: add event loop contract and link api, port mq to new api, cleanup code

* Format Sources

* Furi: cleanup mq and event loop code

* Furi: remove unused staff from message queue

* ApiSymbols: remove event loop from public APIs.

* Fix furi unit tests

---------

Co-authored-by: Georgii Surkov <georgii.surkov@outlook.com>
Co-authored-by: Georgii Surkov <37121527+gsurkov@users.noreply.github.com>

applications/services/gui/view_dispatcher.h

@@ -47,8 +47,8 @@ void view_dispatcher_free(ViewDispatcher* view_dispatcher);
 
 /** Enable queue support
  *
- * If queue enabled all input and custom events will be dispatched throw
- * internal queue
+ * Allocates event_loop, input and event message queues. Must be used with
+ * `view_dispatcher_run`
  *
  * @param      view_dispatcher  ViewDispatcher instance
  */
@@ -101,6 +101,20 @@ void view_dispatcher_set_tick_event_callback(
  */
 void view_dispatcher_set_event_callback_context(ViewDispatcher* view_dispatcher, void* context);
 
+/** Get event_loop instance
+ *
+ * event_loop instance is allocated on `view_dispatcher_enable_queue` and used
+ * in view_dispatcher_run.
+ *
+ * You can add your objects into event_loop instance, but don't run the loop on
+ * your side it will cause issues with input processing on dispatcher stop.
+ *
+ * @param      view_dispatcher  ViewDispatcher instance
+ *
+ * @return     The event_loop instance.
+ */
+FuriEventLoop* view_dispatcher_get_event_loop(ViewDispatcher* view_dispatcher);
+
 /** Run ViewDispatcher
  *
  * Use only after queue enabled