[FL-2797] Signal Generator app (#1793)

* Signal Generator app
* MCO pin initialization in app
* furi_hal_pwm documentation

Co-authored-by: あく <alleteam@gmail.com>

applications/plugins/signal_generator/signal_gen_app_i.h

@@ -0,0 +1,46 @@
+#pragma once
+
+#include "scenes/signal_gen_scene.h"
+
+#include "furi_hal_clock.h"
+#include "furi_hal_pwm.h"
+
+#include <gui/gui.h>
+#include <gui/view_dispatcher.h>
+#include <gui/scene_manager.h>
+#include <gui/modules/submenu.h>
+#include <gui/modules/variable_item_list.h>
+#include <gui/modules/submenu.h>
+#include "views/signal_gen_pwm.h"
+
+typedef struct SignalGenApp SignalGenApp;
+
+struct SignalGenApp {
+    Gui* gui;
+    ViewDispatcher* view_dispatcher;
+    SceneManager* scene_manager;
+
+    VariableItemList* var_item_list;
+    Submenu* submenu;
+    SignalGenPwm* pwm_view;
+
+    FuriHalClockMcoSourceId mco_src;
+    FuriHalClockMcoDivisorId mco_div;
+
+    FuriHalPwmOutputId pwm_ch_prev;
+    FuriHalPwmOutputId pwm_ch;
+    uint32_t pwm_freq;
+    uint8_t pwm_duty;
+};
+
+typedef enum {
+    SignalGenViewVarItemList,
+    SignalGenViewSubmenu,
+    SignalGenViewPwm,
+} SignalGenAppView;
+
+typedef enum {
+    SignalGenMcoEventUpdate,
+    SignalGenPwmEventUpdate,
+    SignalGenPwmEventChannelChange,
+} SignalGenCustomEvent;