Application selection at build time

A list of "user applications" is built at compile time. It contains all the info needed to create the application at runtime (ptr to a create() function) and to display the app in the application menu. All applications declare a TypeTrait with these information.
When a new app must be loaded, DisplayApp first check if this app is a System app (in which case it creates it like it did before). If it's not a System app, it looks for the app in the list of User applications and creates it if it found it.
Those changes allow to more easily add new app and to select which app must be built into the firmware.
Switch to C++20 (and fix a few issues in SpiMaster.cpp and Watchdog.cpp.

src/displayapp/Controllers.h

@@ -0,0 +1,51 @@
+#pragma once
+namespace Pinetime {
+  namespace Applications {
+    class DisplayApp;
+  }
+  namespace Components {
+    class LittleVgl;
+  }
+  namespace Controllers {
+    class Battery;
+    class Ble;
+    class DateTime;
+    class NotificationManager;
+    class HeartRateController;
+    class Settings;
+    class MotorController;
+    class MotionController;
+    class AlarmController;
+    class BrightnessController;
+    class WeatherService;
+    class FS;
+    class Timer;
+    class MusicService;
+    class NavigationService;
+  }
+  namespace System {
+    class SystemTask;
+  }
+  namespace Applications {
+    struct AppControllers {
+      const Pinetime::Controllers::Battery& batteryController;
+      const Pinetime::Controllers::Ble& bleController;
+      Pinetime::Controllers::DateTime& dateTimeController;
+      Pinetime::Controllers::NotificationManager& notificationManager;
+      Pinetime::Controllers::HeartRateController& heartRateController;
+      Pinetime::Controllers::Settings& settingsController;
+      Pinetime::Controllers::MotorController& motorController;
+      Pinetime::Controllers::MotionController& motionController;
+      Pinetime::Controllers::AlarmController& alarmController;
+      Pinetime::Controllers::BrightnessController& brightnessController;
+      Pinetime::Controllers::WeatherService* weatherController;
+      Pinetime::Controllers::FS& filesystem;
+      Pinetime::Controllers::Timer& timer;
+      Pinetime::System::SystemTask* systemTask;
+      Pinetime::Applications::DisplayApp* displayApp;
+      Pinetime::Components::LittleVgl& lvgl;
+      Pinetime::Controllers::MusicService* musicService;
+      Pinetime::Controllers::NavigationService* navigationService;
+    };
+  }
+}